"I don't know"

Months ago, we went through a stage with Jadzia where if we asked her a question and she didn't know the answer or didn't want to answer for whatever reason, she wouldn't say anything at all and would just remain quiet and try to slip away without answering. This frustrated Robby and I so we started teaching her that it was okay to say "I don't know" if she didn't know the answer. And it is usually.

This little lesson has come back to bite me in the butt though. Now, at least 75% of the time, she says "I don't know" immediately without thinking about it. Much of the time I know she knows the answer and can usually turn it back on her to answer me. But sometimes all she says is "I don't know" which drives me crazy.

A particular instance is when she'll start to cry about something. For one, I need to know why she's crying because if she's hurt, I want to check what hurts, etc. For another, if she's not hurt or has a reason (doesn't even have to be a good reason really) to be crying, then she doesn't need to be crying now does she?

I don't want to discourage her from admitting when she really doesn't know and needs real help with an answer (like when she's learning something and truly doesn't know) but I realize now that she says "I don't know" before really thinking about whatever I'm asking - like it's her knee jerk response which isn't acceptable either. Somehow I need to find a balance between the two.