I've had this happen to me a couple times, and I'm never sure quite why it happens. I think it may be through an issue with the Checkpoints where if you go back before the code does something to unbimboify them, they remain bimboified in gallery but not canonically? So unironically the best way to unbimboify Heather may be to bimboify her and then go through that scene until she becomes unbimboified again.
Then again this is just speculation on how the bimboifying works - could also be an oversight, or just a bug caused another way. (Or it could be permanent, and you've simply misread something - it happens!)