My 16 yr old step daughter has come to live with us. need advice!?

my 16 yr old step daughter has come to live with us very recently and i am finding it very hard to cope. my husband works away, i have a much younger child and we live in a remote village. she was having problems at home and school and so we thought it best she come to live with us. however, although i tried to prepare myself for the hormonal maelstrom, i am not sure what to do. she is very angry, aggressive and also very childlike.She has no interests what so ever and refuses to study for her exams. i don't want to resent her being there but my first instinct is to protect my own child. i feel guilty for not loving her like my own.