"Tori feels she owes it to them to try to work it out with their dad, even though it's hard," a longtime friend of Spelling's tells PEOPLE in this week's issue. "They're working on their marriage and they're operating as a family, but of course there's tension. It's a work in progress."
Spelling, who is currently starring in ABC Family's new series Mystery Girls with former Beverly Hills, 90210 costar Jennie Garth, "is very non-confrontational," adds the insider.
"That's her personality. She doesn't like conflict. Dean has always been the big voice in their family. But now? In many ways, this has been great for her. It's forced her to really speak up, to demand to be heard and to say exactly how she feels to him. There's a change in her."
Spelling, 41, who recently told PEOPLE that it will take time for her and McDermott, 47, to work through their issues, is focusing on the couple's four young kids, Liam, 7, Stella, 6, Hattie, 2, and Finn, 1, to stay the course.
"Tori's not a quitter, not even when it comes to something like this. She's going to do everything in her power to make her family whole," says her friend. "If it's going to work out, no one knows. I don't think she knows that herself. But that's the kind of person she is. She won't quit until she's totally defeated."
For more on Tori and Dean's decision to stay married, pick up this week's issue of PEOPLE, on newsstands Friday