Well, it's quite the interesting start and methinks that Dumbledore will very much come to regret this move (I suspect he's trying to strengthen/improve his "tool" with this but the "law of unintended consequences" will not be denied).
As for Hermione, I could see her rather broken state allowing her to take on certain aspects of a Dementor, but I don't necessarily see that as the most likely; rather I can see her wanting revenge on those who did this to her. I rather like valkyrei!Hermione, with or without the chain-mail bikini (frankly, those have always struck me as impractical and unlikely, though easy on the eyes in most cases). Heh, if you want to make it more interesting, you could take inspiration from David Weber's "Path of the Fury" (or it's expanded version, "In Fury Born") and have one of the Greek furies bond with her while she's temporarily out of her mind. The result could be a truly credible partner for the "upgraded" Harry that's going to be coming out of this (I'd wager that magical ash will combine with him in "unexpected" ways and Dumbledore's efforts will yield a powerful tool, but not for Dumbledore to wield but which will rather wield itself).