Lindsay Lohan partied like it was her birthday on Saturday — because it was her mother’s. According to the manager of Mio Posto in Hicksville, L.I., the 26-year-old “Liz & Dick” actress had “double vodka and club soda” during Dina Lohan’s 12-person 50th-birthday dinner. The small but rowdy celebration comes on the heels of the mother of four being accused of being inebriated during a tease for an interview with Dr. Phil (the show will air today). A source says the elder Lohan had wanted to spend her milestone birthday with “just family,” and while her five-time rehabbed daughter and son Michael were present (we’re told 18-year-old Ali is modeling in Korea), so were nine friends, mostly female. The group shared family-style platters of rice balls, meatball marinara, fried calamari, baked lamb, pasta dishes, stuffed chicken, veal chops, shrimp a la crisp (a favorite of both Li-Lo and the birthday girl) and dessert platters, on tables set with roses and surrounded by balloons. “She drank mixed drinks,” the manager tells us of Dina Lohan. “She had a few.” While a spokesman for La Lohan says it’s a policy to not comment on things regarding family, Lindsay’s father Michael, who divorced Dina Lohan in 2007, felt otherwise. “After finding out Dina was drinking in front of Lindsay on her birthday, not only do I think it’s pathetic, but obviously she doesn’t think what anyone thinks of her as a mother,” he told Confidenti@l. “It’s absolutely disgraceful that a mother would appear on ‘Dr. Phil’ in the condition she was in and continue on the same path. Even more troubling is now she was drinking around and with Lindsay.” The insider tells us LiLo’s mom considered having a grander celebration in New York City originally, but things “didn’t pan out.” After dinner, we hear the Lohans took the party back to their private residence on Long Island to continue the festivities.