Sora belongs to
Lightning Storm belongs to
Rhymeheart belongs to
My Little Pony © Hasbro
It's not that uncommon for people who play team sports to shower together. It's not really a shower where you relax, take your time and enjoy it, but a functional one: soap, rinse, get out.
It's more efficient to build joint showers in changing rooms and people who are sweaty as hell don't wanna wait until they get home to take a shower.
Girls and boys have separate showers, of course. Not that it would matter much in a nudist world such as Equestria.