According to Official Guinness Records,
The youngest female with a full beard is Harnaam Kaur (UK, b. 29 November 1990), aged 24 years 282 days when she was confirmed to have a full beard, in Slough, UK, on 7 September 2015. Harnaam's portrait as included as part of the #Project60 champaign. She is an avid body confidence and anti-bullying activist. Full story: Video - Youngest female with a full beard shares inspiring story of journey from bullying to empowerment
For a complete list of 2015 records, please visit 2015 Guinness Records in United Kingdom.