so my 6yr step daughter just told me that she is now showering with her 17yr step sister when she is at her mothers house. She said nothing inappropriate has happend but is this really okay? A little back ground they have only been in 3ach others life for less then 1 1/2 years and have never showered together tell recently and the 17yr has never given her a bath or shower
Some teens can be extremely modest and self conscious of their bodies, but many take a very relaxed view of non-sexual same-gender nudity, and especially if it has become pretty normal for them (for example, if on a sports team it's common to shower and change in front of teammates with little privacy, the same is even somewhat true of theater and dance groups, who often have to change costume in a fairly small room and with limited time between dances/scenes). I have known of college students to share a shower just because there were not enough shower cubicles and everyone had morning classes.
It's also normal and not considered inappropriate for family members to see each other unclothed in many cultures, for example in places with sauna or communal bathing traditions. In general, my view on casual family nudity is that it's fine and healthy as long as everyone involved is comfortable with it.
That said, the fact this is a new behavior and you seem uncomfortable with it is probably reason enough to ask them to please shower separately, without making any accusations or embarrassing the girls. I think there's a high probability that it's innocent, but of course there is no way I can know that with certainty.
Listen to your instincts. If your gut feeling is that this bathing arrangement isn't right for your daughter, don't ignore it. It's reasonable to set a boundary at not letting siblings shower together.
From a United States perspective this is something you should definitely do your best to stop. These kids are not sisters and there is simply too much possibility for abuse. My wife is a early education major with 20 years teaching experience now. This situation is a HUGE RED FLAG for her. It has nothing to do with trust or gut feelings, but rather making rational decisions to protect your child. Reduce the opportunity for abuse when possible, and this is that time.
This also has the provided benefit of letting your child know you care for and love them and will take steps to protect them. Kids don't also immediately show appreciation for restrictions in their life, but they do respect it. As they grow older they will benefit and appreciate what you went through for them.