Boston police have arrested a Dorchester woman after another woman was dragged by a car, then struck by a taxi in the South End early this morning, leaving her in critical condition.The victim, who police said is 29, was dragged "a substantial distance" by a car driven by Brianna Smith, 26, of Dorchester following an altercation outside the Victoria Diner on Massachusetts Avenue at 4:30 a.m., police spokeswoman Officer Rachel McGuire said.The woman and Smith's car were then hit by a passing taxi, McGuire said.McGuire said the fight involved four females.