When a girl says she is still thinking what does she mean?

Well, I think that I would take that at face value... she will think about it.

It could also mean no, in cases where the girl doesn't want to be cruel and reject an idea outright, but either way, that sort of language means, basically... back off, don't push.

it means girl really want to think about him, if she want to say NO, than she never says that she will think.

She really thinks about him and than remember last moments she passed with her boyfriend and than after decides that Is he right person for her or NOT ? and than she tells final answer to him.