i agree with everyone here, but i'm not a really talkive person in real life. i usually listen in. you should tell ur friend that u rather not answer "those" kind of questions but other questions would be acceptable.
see if she will be open to asking more general questions rather then personal questions.
also, when someone asks me a question like that i usually change the subject and if they asks me why i changed the subject i usually tell them that id rather not answer that. it may make her mad but she should have some respect for u and ur personal space.
hope this helps and best of luck.