The former co-owner of a private medical transportation service for the elderly has pleaded guilty in federal court to Medicaid fraud. Kori Ann Donovan, 41, admitted Friday in U.S. District Court to defrauding Medicaid from 2008 to 2012 while running Advanced Care Transport. She admitted billing the government health care program for some rides that never took place and inflating the mileage on others in order to increase reimbursement. Her actions cost the government between $2.5 and $7 million, according to court documents. Donovan will be sentenced in July to one count each of health care billing fraud and aggravated identity theft. A.C.T. shut its doors last September, but the corporation has been named a co-defendant in the case.