Mine is the same way. She's fine in a swimming pool, but just seems SURE we're going to dump buckets of water down her face. And she will. not. sit down in the tub.
For some reason, having Daddy do it instead of Mama helps some. (I guess she doesn't trust me? lol) But usually we have to just tell her to "look up" - and then be really, really fast...and repeat....