restore phone question

I'm trying to restore my daughter's Iphone 5 that stopped working recently where text messages are concerned and even though all photos have been dumped, it still wont restore telling us that there isn't enough room. It indicates that there's a ton of 'documents' on the phone and we can't figure out where these documents could be. We've dumped all pictures and videos and the phone still shows 3/4 full. Anyone else run into this? I guess we'd like to just erase everything and restore a prior backup but keep getting kicked out that the phone doesn't have room.