There is a dependant relative credit but this is for supporting a relative who is incapacitated by old age or infirmity. You do not mention the mother being incapacitated in any way, and at 59 she is too young to qualify. The credit is very small anyway.
Your girlfriend may be able to claim tax relief on any medical expenses she has paid on her family's behalf, even when provided overseas. In 2009 relief is only given at the 20% rate, so again, this would not be worth much.
Not much help, when it must be quite a financial burden.