Mandy has been employed in the Valuation Office since 1988 working predominantly in local taxation, particularly non-domestic rating. In 1997, she became a Chartered Surveyor and in 2018 she gained the Rating Diploma.

Mandy has undertaken various roles in her career including case worker, team leader, and technical adviser. In 2017, she was part of a small team who rolled out CCA throughout England. In 2019 she became a technical adviser with a major part of the role being management of litigation cases. During her time as a technical adviser, Mandy worked with colleagues across government on the fundamental reform of business rates which resulted in the Non-Domestic Rating Act 2023. In 2026, Mandy became Head of NDR Technical.