After all, her younger brother had just given his number to Melissa Joan Hart.
"He tried to play it all cool, but he knew who she was. I screamed and I told my friends, 'My brother just met Melissa Joan Hart and she asked for his number,' " Wilkerson, 37, tells PEOPLE exclusively.
When the couple eventually traveled to Alabama to visit the Wilkerson family, they were welcomed at the airport by an ecstatic Sally, who jokes that she was "a crazy person."
"I was like, 'Oh my gosh, Sabrina the Teenage Witch is coming!' " she says. "I made her sign everything. Mark said, 'Don't you dare.' "
Little did Wilkerson know, her signed memorabilia was only the beginning of her deep-rooted relationship with Hart.
Childhood MemoriesGrowing up in the South, Wilkerson was surrounded by sweet tea, fried and fatty foods – but she was also born into a fit and genetically-blessed family. Her mother ran a dance studio, her sister was a cheerleader and a beauty queen, while her brother was incredibly athletic.
"Mark never went through a gawky stage in high school," she shares. "My mom's a dance teacher. My dad never understood how somebody can have an addiction to food. He has that CPA philosophy – you want to save money? You don't spend. You want to lose weight? You don't eat."
The culmination of it all sent Wilkerson in a tailspin and by high school she hit her heaviest weight of 287 lbs., hiding junk food in her closet and visiting the local Dairy Queen for ice cream, French fries and chicken fingers.
"I knew that teenage girls borrow dresses from each other. I couldn't do that," she says. "I had to shop in different stores than my friends. I would go to my best friend's mom's closet and wear a pair of her jeans."
A photo taken when she was 19 changed it all. "I saw a picture of myself one Christmas and I turned to my mom and I said, 'I'm fat,' " she recalls. "I didn't realize I really had a problem until I saw that picture."
Losing the WeightWilkerson stopped eating fried foods and replaced her sweet tea with gallons of water, but it was her supportive coworkers who initially kept her going.
"I worked with a group of women in their 40s and 50s and they said I'd lose the weight," she explains. "I lost 26 lbs. in the first six weeks and with that came the motivation, because I had the support. Then I started working out. Within that first year, I lost 75 lbs."
Wilkerson's since lost a total of 136 lbs. – and kept it off.
And now, for those who once referred to her as Big Sal, it's shocking to see her total transformation, which includes her new title: certified yoga instructor.
"When I go home, everybody expects you to gain the weight back over a period of time. To this day they go, 'Oh my gosh, you kept the weight off,' " she says. "Nobody would have expected Sally would be in the health and nutrition field – they would have laughed."
Fast-forward to today and that initial meeting with Hart – who wed Mark in 2003 – only further motivated Wilkerson to continue on her quest to a healthier lifestyle.
Family SupportTogether, the two have learned to lean on each other for support as Hart has faced her own struggles with her weight, most recently partnering with Nutrisystem to shed her pregnancy pounds after welcoming her third son, Tucker.
"We're good for each other – Melissa's career revolves around her being in front of the camera. That's always an issue for her, so she's supportive of where I've been. She's not going to judge me for my slip-ups," Wilkerson says. "I'm into fashion so she calls me and says, 'How does this look on me?' We can FaceTime and it's fun – we don't sit down with a bag of chips."
And no time together is taken for granted as both Wilkerson and Hart see shared family getaways as an opportunity to inspire one another.
"When we go on vacation I tend to go, 'This is my excuse to pig out!' But I see what Sally is eating and I'll order what she's ordering. It keeps me on track," Hart, 37, tells PEOPLE. "She's lost an incredible amount of weight and she's able to maintain it. Sally doesn't deprive herself – but she's good about balancing it out with really healthy things."
Hart says her sister-in-law's dedication is nothing short of impressive – especially when it benefits her. "On my birthday last year, I went crazy on cheese dip and cake," the actress admits. "But Sally's so disciplined and I just follow her lead. She'll say, 'I'm going for a run' and I'll go with her."
As for Wilkerson's confidence, Hart adds, it's contagious. "Sally taught me that you want to feel good about yourself. When she first started losing weight, she got compliments and they drive you to want to do more."
And for the mom-of-three, it's worked: Hart has lost a total of 35 pounds since giving birth to her now 15-month-old baby boy.
"I'm proud of myself, I feel great. I want to look fantastic for my husband. He's in incredible shape," the Melissa & Joey star says. "The three of us together, it's, 'When are we going to the gym? When are we going on a walk?' "
Once they're all caught up on fine-tuning their fit figures, Hart admits there's still plenty to discuss in their personal lives.
"Sally's my marriage counselor. She's the only one that understands Mark! I can talk to her about anything – she helps me navigate the in-laws," Hart jokes.
For more on Sally Wilkerson and Melissa Joan Hart's weight loss journey, pick up PEOPLE's Half Their Size issue.
Reporting by MONICA RIZZO