Hi J.,
You are asking for opinions, so I am giving you mine. I agree with Maggie. However, here is my take. If you don't ever start a habit, then you don't have to break it and it is easier on everyone all the way around. I don't feel it is appropriate to be getting in the shower/bath with a daughter. I do have a son, so that is really not an issue in my household, but my son is about to turn 4 and has already asked questions, but whenever my son gets in tub with his dad now, my dh puts on swimming trunks. His Dad has always been the one to give baths to our son; that is their bonding time. My dh allows him to play and dawdle in the tub. Wheras, at that point of the evening, I am tired!! I just want to get him washed, cleaned up and out of there!! So he of course prefers his Dad to bathe him. My dh rarely if ever takes showers with our son. We really try and avoid that.
I am sure he will give him his bath forever until he ask him not to, and of course my dh answers any questions he may have about body parts, etc., whatever as simple as possible.
With girls, I just don't feel it is appropriate to be doing it together. And once you start, then you have to readjust or do something different and you can just avoid that all together if you don't start it. I think it is fine for a Dad to bathe a child (girl or boy) and certainly to teach them how to, but getting in the tub/shower with them, no.
Thanks for allowing me to express my 2 cents worth!
Gladys