

I would be fine about being asked, asking wouldn’t affect the relationship, but I would say no because I don’t want it.
If they did it anyway, or without even asking, I would end the relationship and probably make a police report. How many other boundaries are they willing to cross or have already crossed? Is there a camera in my shower? It would make me incredibly worried to deal with that level of disrespect.
We can’t fix other peoples issues for them.
We can choose to support them if they are actively trying to fix their own issues.
We can also decide that even though they are trying the impact is too big on us and distance ourselves.
But if they aren’t actually trying to better themselves there is nothing we can do except protect ourselves.
Your sister needs to look into co-dependence and trauma-bonding (if not in this case then for future reference), and focus on becoming emotionally independent rather than confusing nurturing with doormat. She can only fix her own issues, not her friends. And learn that not every friend is worth the title.