According to the dictionary the word "bonne" means housemaid in English and its origin is French from the late 18th century. The term derives from the French feminine “bon” which means good.
The following link leads you to the Oxford Dictionary:
The bonne is a maid and works in Mme. Clopin’s Pension Suisse at Passy. Andora also has to “[…] spy on [her] for possible negligence or perfidy.” (Lewis 188)