I'm surprised she did not request this information prior to starting the therapy, usually you get that out of the way at the start. But now that you have already started I agree with KisselJ that terminating in treatment for this reason is not appropriate.
As far as overreacting, based on this information I don't think so, again, if she has worked with you for a period of time and then all of a sudden makes such a request it is going to catch you off guard and spur such a reaction.
Unfortunately, it sounds like you weren't able to express your concerns and feelings about this situation when she brought it up. Or maybe you have and just didn't write about it in your post. that would give us insight into possible motives.
However, ulitimately its up to you, you must weigh the cost/benefit of working with this therapist, who you've stated is amazing, and fulfilling her request that you regard as an excessive probing into your personal records and doing so at the wrong time during the therapy.