I'll be teaching the first session of my next Writing Young Adult and Children's Fiction class starting next week, and was preparing by looking up some popular ice breakers. It's important in a writing class for members to feel comfortable sharing, so I always try to spend a little time at the first class getting to know each other. One popular exercise is to break into pairs and have each person interview their partner, then introduce his partner to the rest of the class. You might ask your partner about her job, or where she grew up, or what hobbies she has. But really, you only get to know your partner by asking why.
Here's an example. You could ask your partner if she has any pets and she could say she has a pet iguana. That's kind of interesting. But if you take it a step farther and ask her why, you might find out she always wanted to have kids but got divorced before that happened so now she has her nephew come over for the weekend once a month to let his parents have a date night and he loves iguanas so she got one from the pet store and they study them together. Now that's a story. What's the difference between the first answer and the second? You asked why.
Now translate that into your writing. I can guarantee you'll discover something interesting about your character that you hadn't thought about before and makes her a more real person. Never have three little letters held so much power. So go ahead, ask... Why?