March 2nd 2010

By Lisa Ingrassia

Its no secret that Shannen Doherty has been asked to join Dancing with the Stars in the past and swiftly turned down the offer that her former 90210 costars Ian Ziering and Jennie Garth happily accepted. I have a huge fear of live audiences, Doherty explains. I break out in hives, full blown panic attacks, and everything else.

So why did the she finally cave? Doherty, 38, tells PEOPLE that she was inspired to take on the challenge after her father suffered a devastating stroke on Christmas Day. He lost his speech, he wasnt mobile, she says. He was really struggling, and still is. When I mentioned this to him, he got really excited, and he wanted me to do it. I thought, if my dad can fight through having a stroke and the loss of being able to communicate, I think I can do this for him. So I figured Im going to get over my fear for him.

Doherty has more than a fear of live audiences to overcome when she appears on the shows 10th season premiere on March 22: She hasnt hit the gym since her days on Charmed. I dont work out, she says. I need to get my endurance up.

Doherty says she doesnt have much dancing experience beyond taking tap classes as a kid, but shes excited for the challenge. Im going to get in great shape, and everyone who I know whos been on the show has had a great time, she says. Its with hesitation and fear, but its going to be good to conquer a fear.