She's just drinking too much to fast, in my Opinion. I have a hypo girl that's going on 9months old and I still have to watch her in the water otherwise she does it every time
. Last time she did it I thought she was going to die from trying to hack it up, her mouth got blue and everything X.X...some stimulation and yelling later she popped back up and was fine. O.O*heart attack* I now guard her from drinking as much water as she possibly can while bathing EVERYTIME. She hasn't done done her hacking choking dance since.
I would just watch her and make sure she's not chugging the water...