are you sure she got a visit visa and not domestic worker visa ??
shes not allowed to work at all on a visit visa, her employer could be fined £10,000 !
anyway contact these people for advise
For overseas domestic workers who need confidential support and advice in the UK contact:
Kalayaan UK St. Francis of Assisi Community Centre
13 Hippodrome Place
London W11 4NQ
Telephone: (+44) (0)20 7243 2942
Email: info@kalayaan.org.uk
Website: www.kalayaan.org.uk