To shorten the bath, I suggest doing it with something to look forward to afterwards. That is, don't do it right before bed! :) Do it with a video set up, so that the bath, which is pleasant, can be done in a reasonable time.

I have also used timers a lot. I use them in a non threatening way, just to let my neurotypical and asd girls know what's a reasonable amount of time to spend on something. You can get a wind up egg timer, but the ticking can be annoying. Put it right outside the door, but be sure to warn them when it's 3 min, 2 min, about to go off (most hate suprises). So, time to wash. Time to rinse, etc.

Re: the control issue. You can get inexpensive glycerin soaps that are nearly clear. Scented or unscented. Then: if you move quickly, you can pick what color soap you use. If you do x, you can pick the sample sized shampoo you use, etc. etc. These guys live in a world that is very confusing and mostly beyond their understanding. If we let them pick the mini shampoos, mini conditioners, little soaps, etc., and have THEM set the timers, and pick a short video to watch when finished...the whole bath/shower thing can become less of a struggle.

But most parents of teens will tell you it's a struggle even w/ntypical kids. Then you may just have to sit down and say, I love you but I don't love how you smell. And it's not socially acceptable. (and take the stinky clothes away at night and put them somewhere. Brace for the explosion).

Been there...done that. Kid's in college now, and mostly (!) showering. :)

Amy

My 12-yo son did not like showers or baths, until he figured out the shower in our master bathroom was different than the other bathrooms...had to do with the noise/spray. He will take showers now, but only if I remind him, warn him that it is going to happen, nag him, and check that he really does it and not just splash some water on himself...we also have the trouble getting him to brush his teeth or change his clothes...both totally unnecessary things to do according to him. It has gotten easier to get him to change clothes once I figured out what he likes to wear...loose, no collars, nothing tight...

Will she take a bath? My son says showers hurt his skin. This could be a sensory thing.

Its awkward when they get older...but we still have to supervise the ahower. Try printing out, or making up a short, to the point..step by step instruction sheet for the shower...laminate it and hang from the shower head...they tend to be driven on a ocd level to follow charts and instduction sheets...use it to your advantage

Ear plugs..a step by step instruction guide for showering..with pictures..have it laminated and fasten or hang from shower head...I have to enter and supervise due to same problems you have...and it is awkward with an older child. Good luck!