The former Fat Actress says she's working hard for her swimsuit debut on Monday

Kirstie Alley is due to pose in her bikini on Monday’s Oprah Winfrey Show, almost a year to the day after she first promised Winfrey she would.

On Nov. 7, 2005, the former Fat Actress star and Jenny Craig spokeswoman told Winfrey about losing 55 pounds and, inspired by a guest who’d lost 70 pounds to become Miss Bikini America, said, “You know how I said every 15 pounds I have to challenge myself? I’m thinking this would be a really good challenge. If I don’t make it, I’m really sorry. You can all come over to my house and see me in a bikini. But I think that would be a grand challenge.”

Why take on such a challenge in the first place? “I’d like to prove to myself and maybe other women my age that there can still be good years ahead of us,” Alley told PEOPLE in June. “Maybe even the best.”

Still, she admitted it was a bold move. “At my age, can you really turn your body into a bikini body without having surgery?” she wondered. “This is an experiment!”

One that she wouldn’t have agreed to if not for the support of her children, son True, 14, and daughter Lillie, 12. “I said to my kids, ‘Can I do this? Will I embarrass you?'” she recalls. “They were laughing about it.”

In her blog on the Jenny Craig Web site, Alley writes that she wanted to get back in bikini shape because she was once a competitive swimmer and “spent most of my life either in a Speedo (yikes) or later in a bikini,” and because “my kids are always in the pool or the ocean or some lake beckoning me to come in,” and she was afraid paparazzi would snap an unflattering shot of her.

“The most important reason I want to wear a bikini on Oprah, however, is because if I, a 55-year-old woman, can look even halfway decent, imagine how all of you could look in a bikini,” she continues. “Hell, I’ll never look like Giselle, I never did! But maybe close to Bridget Jones or a Dove girl or something that is just fine and healthy and happy, with no surgery, no lipo and no drugs – that’s saying something!”

She also writes that she’s been working hard to get in shape for her bikini debut. “I’m walking vigorously (hiking) every morning for one hour on these big ole hills by my house. Then I try to get in an afternoon workout of weights, circuit, palates or yoga. The a.m. thing is like clockwork, the afternoons are hit and miss. But that’s my goal this week: two times a day for five days a week until I do the show.”

How did Alley put on the weight to begin with? She told Winfrey a year ago, “I made some good decisions simultaneously with some bad decisions. The good part of it was, ‘I’m going to spend more time with my kids and I’m going to cook.’

“The bad decision was – and this is the dumbest decision I’ve ever made in my life – it went like this: If a man really loves me, he will not have to love me for my body. He will really love me just for me. When did I decide I was a big, fat girl?”