Here are some things I would try:
1) Begin each question by opening up yourself. Offer her something personal that's a bit deeper and more open than what you'd like from her. If she sees that you are willing to make yourself vulnerable to her, she'll feel more comfortable opening up to you.
2) Try talking to her gently at night in a quiet room with the lights off. It's easier to open up when there's no expectation of eye contact or appropriate body language.
3) Offer her multiple choice questions. "Did you have a good day or a bad day?" Perhaps she doesn't offer firm opinions because she always feels a mix of opinions and needs encouragement to average and summarize them.
4) Her emotions may be complex and she may not know how to express them concisely. Keep your questions simple and follow each of her answers with validation and a branching question that allows her to refine her answer. "I'm sorry you had a bad day. I hate it when that happens to me. Did something bad happen to you or did something bad happen to someone else?"
Good luck! If you find an approach that helps, please let us know!
