I think I'd talk to her father first and tell him that he's going to make his daughter a social outcast if he doesn't get on top of washing, cleaning and telling her she needs to sort her hygeine out. You both need to be singing off the same hymn sheet.
I wouldn't be shy about washing either, your house, your rules and washing gets done at your house. I would also be showing her how to do her own washing so if dad doesn't step up, she can sort herself out.
Can you have a word with school to see if they can cover hygeine and cleanliness in phse lessons?
Is she is funny about perfume smells her her an unscented distant and see if she will wear that.
Lack of cleanliness can be a sign of depression, is that a possibility, can you help on that front?
My son went through a stage of smelling of BO, he was sent back to the shower and told in no uncertain terms that he stank, every time. He didn't like it or, neither did I but why should I have to put up with the stench. One thing that did help a bit was moving to a proper soap bar rather than shower gel, maybe you could give that a go?