So it turns out she had disabled her imessage account a couple days ago, but the problem persists.
She came over last night and I messed with it and can't figure out what's going on. I wiped the Messaging apps cache and data, but it didn't help at all. I witnessed all the weird things it does. Sure enough, when you delete a thread it creates a new one at the bottom to that same person with the date of 12/31/1969.
I tried downloading Verizon Messenger to see if that would work, but it has the same problems.
Without doing a factory reset at this point, I don't know what to do.
Since the problem is not confined to a single messaging program, I'm thinking something must be corrupted at the system level with messaging.
Does anybody have any idea how I can completely wipe the messaging app and start over without root?