Just wondering what you found to get through your daughter's tangles.
I went through this with my youngest when she was 6 or 7. She always insisted she comb her own hair and quite honestly, it looked good. She too has fine hair, and lots of it!!! One day I decided to really comb it well and found what you did. I about flipped. The only solution for us was to cut the underneath out. Now, she does keep it shorter underneath to prevent this from happening again. I can relate to your story; it was a nightmare!!
Hope it all worked out.