Loved Free Spirit's advice (and signature) !!!
It takes a lot for anyone (children included) to relax and trust enough to share what is bothering them (assuming they are even consciously aware of it). Personally, I'd try to create a relaxed environment - disassociated from ANY connection to the "issue" at hand... Then, when you feel your daughter might feel comfortable and "safe" - gently wrangle the discussion towards her feelings ~ with luck she'll start to open up... These things can seldom be forced...
I hope that helps !!! ~ Ben There