According to Official Guinness Records,
The fastest marathon dressed as a chef by a female is 4 hr 54 min 49 sec and was achieved by Helen McWilliams (USA) at the Akron Marathon in Akron, Ohio, USA, on 24 September 2016. Helen has participated in the Akron Marathon for seven years. She loves to dress in costume and has wanted to break a Guinness World Records title for as long as she can remember.
For a complete list of 2016 records, please visit 2016 Guinness Records in United States.