It would depend on the child's parent.
I had sleep overs for my daughter this summer at our house, and she is 7.
I told the Moms.. to make sure their child is bathed, BEFORE coming over to drop them off at my house.
OR... I also told them... IF their child needs to shower while at my house.. ."Is it okay with you?" and "If so, do you want your child to shower/bathe alone or is it okay that she and the girls all shower together???"
I simply asked the child's Mom.
AND I also asked my Daughter, how SHE felt, if that scenario occurred.
Ultimately, you need to get the "Okay" from the child's parents.
Each family has their own 'rules' about showering/ages/what they think is appropriate or not/cultural differences etc.
It is up to the child's parent/Mom.
If you do not clear it with them first... then possible conflict can arise.
So just avoid that... and ask the Mom(s) of the child, first.
When my daughter is at her friend's house for swimming... after the Mom has them shower. Which she asks me first, if it is okay. THEN she has the girls shower, with their bathing suits on.... if together. But ultimately, they do it separately. It is just that Mom, respecting my daughter's "privacy" and Mine, as her Mom.
all the best,