There's a new sexagenarian in town and she's feeling good: On March 31, Tony winner Linda Lavin -- who served up thousands of blue plate specials on CBS' long-running sitcom Alice -- storms into The O.C.'s Cohen household for a Passover seder that'll make last year's Christmukkah feast look like, well, a day at the beach. ''Everybody's terrified of her,'' laughs Lavin, who plays Sophie, the ''liberal New York socialist'' mother of Peter Gallagher's Sandy. The New York part isn't a stretch for Lavin, who was a Broadway fixture (The Tale of the Allergist's Wife) before launching her traveling one-woman cabaret show. She admits that she had ''no idea what The O.C. meant. I thought it was a medical show! I had to call a friend who said, 'Um, it's only the biggest hit on TV right now.''' She quickly bit, much to the delight of her two teenage grandnieces. ''It doesn't matter that I've been in the biz for umpteen years. They're now familiar with me for the first time, screaming on the phone, 'You got to meet Seth! You got to meet Ryan!' Finally, I've made it.'' Welcome to The O.C., Grandma!