On 14 September 2015, she reached her career-high singles ranking of world No.

Ghent-born Mestach won the junior events of the 2011 Australian Open in both singles and doubles.

In 2012, Mestach made the final of one ITF event and the semifinals of two others.

Playing for the Belgium Fed Cup team since 2010, Mestach has accumulated a win–loss record of 9–6.

She has also spent time on the professional padel circuit[1] and in that sport, she represented Belgium at the 2023 European Games, playing the women's doubles with Helena Wyckaert.