Loss of progress

More likely a loss of what relic level you remember taking them to. I've never seen a documented case of this in 7 years on the forums and in game.

Did you use her at any point in GA? If you did, go back and look through your history and post a screenshot of her as R8 and now R7.  

I think this is also a case of misremembering, they announce when they're doing a toon reduction and it wouldn't be a single relic level, it doesn't make any sense to do a random individual.