“Either the shower takes an hour or it doesn’t happen at all, and I can’t say a word without a fight.”
Hygiene battles are almost never about hygiene. Their body is the most personal territory they have, and control lands hardest there. There’s also a distinction worth drawing before you pick a move: a teen who avoids the shower and a teen who lives in it for an hour are usually solving different problems. Avoidance is often a starting problem or a comfort problem. The hour is often decompression, hot water and privacy doing real work on a hard day. Same bathroom, different needs, different moves.
Choice-Within-Limits holds both. You name the household need without apology. They own how they meet it.