"Davidwest" / interesting relation of your experience at age at the house of a friend with his older sister aged of who was in charge of you for two days and as she was angry not to be free, she abused a little of her power on you , especially for showers where according to your relation she succeded in forcing you to stay naked in front of her frontally and back when you walked from the other part of the house towards your bedroom stark naked whith her behind you with a perfect view on your naked butts.
I am amused by the fact that she was "the boss", deciding when you needed a shower, where you might undress, when going out of the shower, giving you towels to dry, leaving you naked to come back to your bedroom to dress again and following you during your walk.
a wonderful experience and apparently she enjoyed to have such a power on younger boys but not small kids, after all you were 13 age already and her only 17 age !
but at that time I guess that the prents were almost all thinking that a girl was much more mature than boys and that her behavious was fair and normal.
I have noticed that your friend did not complain, may be for him it was routine !
while having no sisters it was new for you.
Did you have complained to your parents after that week end or were you too embarrassed to relate it?
Anyway, it is a kind of CFMN situation, not too bad but embarrassing of course and personnally I would have not liked it at 13 age because she was not so older than you and certainly not an adult, not the same as if it were a aunt !