Mary Ann Eagin is the villainess from "Murder at the Finish Line" She is the owner of Eagin Racing, but she was revealed to be having financial problems. She used the money raised for her team to cover her losses, but she oversold her shares to various investors.
Once Matt Thomas, one of her noted racers, started winning numerous races, Mary Ann turned heel and set out to stop his winning streak, mainly to keep the investors from wanting a return on her money. She poisoned Matt hours before his race, and to make sure he would be killed, she sabotaged the engine in his car, leading to his crash.
After the team was successful in getting a new engine working properly, the evil Mary Ann snuck into the garage later that evening and sabotaged it, pouring an explosive into the engine. Mary Ann's reveal came when she ducked for cover while the engine was being tested, and she was arrested for Matt's murder.