It was the morning of Stella Ritter's fifth birthday. Her father, John Ritter, was due on the set of his hit ABC sitcom 8 Simple Rules later that day, and her mom, Amy Yasbeck, was getting Stella's backpack ready for her first week of kindergarten. But first they were intent on fulfilling their daughter's only birthday wish: to wake up with Peekaboo, her new tabby kitten, snuggled beside her in bed. "For John and me, it was this big deal," says Yasbeck. "We were like, 'Quick, sneak in Peekaboo, don't wake Stella up, put the cat here, position it, oh God no! Quick!' trying to get the cat to calm down and lay there by her head. But we did it." Soon Ritter himself was down on all fours, pretending to be Clifford the Big Red Dog, the character he voiced in cartoons, as Stella opened presents and the family reveled in what had always been their favorite time of year. "We were in September mode," says Yasbeck. "For us that means Stella's birthday, my birthday, John's birthday, our wedding anniversary. Everything for us happened in September. Everything, as it turns out."

Later that night, at 10:48 on Sept. 11, 2003, John Ritter died on the operating table at Burbank's Providence St. Joseph Medical Center as doctors tried to repair a dissection, or tear, in a previously undetected aneurysm in his aorta. He had called Yasbeck from the set that afternoon, complaining of nausea and chest pains, and asked her to meet him at the hospital. Just before he was wheeled into surgery, they told each other "I love you" for the last time. It was six days shy of John's 55th birthday.

Now Yasbeck, 42, is returning to work, starring in the new FOX sitcom Life on a Stick. She has also been pursuing a lawsuit against the hospital, claiming that inadequate care resulted in John's death. But her priority remains raising Stella and helping John's other three children—actor Jason (Joan of Arcadia), 25, and college students Carly, 23, and Tyler, 20, from his first marriage to actress Nancy Morgan—cope with their father's death. She sat down with PEOPLE's Elizabeth Leonard to talk about her tragic loss and the power of the love they shared.

It was the worst thing that ever happened. Stella's brothers and sister are the only ones that are privy to what that next day and those moments were like. I didn't even talk to my family about it. It's huge. It's life-changing stuff. It's like war stories. I think you are immediately and forever altered in your way of thinking. The "things" are all reminders, whether it's a stack of his books or a closet full of clothes that brings you to the point of sadness. But you can go to the place in your heart where the person still lives and kind of touch the real reason you were with that person. When the "things" get rearranged and dispersed or given to Goodwill or meticulously kept, you realize that none of that really means anything. They are lovely reminders, but the real thing can't be divided, dispersed or given away.

I gave books to a lot of people—to my family, to his family, to his friends. Every time the kids come over, there are things I've found, little knickknacks or books or little notes to them. I sent almost all of John's white sweat socks to my nephew Mark, who was serving with the 101st in Iraq. He wrote something saying, "We need socks out there!" So he wore John's socks out in the desert. That's pretty cool. But it's too hard to go through everything. That puts a person on the floor for weeks if you do that. I kept old love letters. There's more than plenty I kept for myself. With Stella, instead of making a little box and me choosing things for her, I've saved so much stuff for her to be able to decide what's important for her. Like the shirt he wore at the hospital in the delivery room when she was born. She's going to have that so when she sees the pictures of her dad holding her for the first time, she'll be able to wear his shirt. He wore a blue T-shirt that I had picked out for him. Stella can make her own treasure chest.

For Stella, me and the big kids, our relationship with John is still unfolding. There's no making your peace with it. There's a rainbow of emotions, and the minute you try to pin yourself to one of them, the next one comes along and knocks you for a loop. Stella and I paint and draw and write poetry and write in journals and write little books about Dad. Stella is working through it at her own pace, and I'm just there to be in awe of her and to learn from her and to catch her if it gets too overwhelming or too confusing. She had to go back to school, though, three days after her dad's funeral. The school was so new to her anyway, and it's basically every kindergartener's nightmare when their parents drop them off at school that they're not going to come back. You can't impose your own grief process on a 5-year-old kid who's having their completely private experience. Everybody really rallied around Stella and did their own thing at the same time.

John had specific relationships with each of the kids and with Stella, even though he only knew her until she was 5. Many of our home movies from when she was a baby have John reading the classic original Clifford story to her, and then he went on to do the voice of Clifford in the cartoon. She can hear him doing Clifford. And in our car, we have one of those tape recorder things built-in above the visor, and once when I was in the car, I had listened to it accidentally and it was John singing "Chantilly Lace," and it starts out "Hellooooo, baby...." The next time, I was in the car with Stella, and I asked her if she wanted to hear it and she said yes.

He poured so much love and time and energy into being Stella's dad—and the big kids backing that up all the way, just completely loving their baby sister. When he died, everyone—the big kids, certainly, but even Stella—got a huge piece of his spirit. When all four kids are together, you can really feel him.

It's comforting to know that there are other people out in the world that are going through losing him too. I can look across the room and somebody gives me a look, and I know. Sometimes they talk to me about it, and sometimes they won't. But you can get that instant connection. It's not just me going through my healing process or my family's healing process. Our family has to go through other people's healing about John. People really feel like they lost somebody, whether they knew him or not, and I don't take it lightly when somebody tells me their story of the first time they saw him or the one time they met him. It's huge to them, and I totally get that.

I'm not ready to start dating again. I'm not sure I ever will be. Not one of my family or friends or anybody who knows me to any degree has asked me about being set up. I think they know me well enough to know it doesn't even cross my mind, so it doesn't cross theirs.

There's no real formula for grieving, and that is the lesson: It's okay to be wherever you are with it. John taught us a lesson every day. He'd walk down the sidewalk, and instead of just looking at the nicely manicured bushes in our neighborhood, he'd point out the weed growing up through the sidewalk, and he'd say, "That's life. That's what life does. You put the cement over it, you do anything you can, and life always comes back." You go on with your life, like a weed popping up through the crack in the sidewalk. You can't lie down and go, "My life is over too" as much as you may feel like doing that—which I do a little bit every day. I keep going for Stella. It's a huge lesson for her to know that it's okay to be alive and to go on living and that it honors the person to live with a little bit of their light inside of you. You can't live a hollow life. I can't. Especially for Stella.

In talking to her about her dad dying, I can use a lot of her dad's philosophy about life, which is very important. So it wasn't like I was scrambling to read books to figure out something to tell her. It was all already there. We had been living it the day before, we had been living it the day he died, and we continue to live it: Life is precious. It was a gift that he had been giving Stella forever and still gives her.