See my blog on 100 questions to ask your boyfriend
Make her feel comfortable, and try to find out reasons for her actions and reactions. It is also good to ask her about yourself and how she looks you in her life. You can also present some hypothetical scenarios, and ask her how would she feel if you react to some situations in a certain way, and if sometimes you don't have enough money to make both ends meet?. This will help you know about her nature, and if she truly loves you. It is good to know about her friends to determine her liking and disliking.