I'm hoping I post this in the correct forum and apologize in advance is it's not.

My girlfriend and I made the choice to merge our two families. Myself, a medically retired 44 year old single father of a 13 year old son and my 45 year old girlfriend and her 15 year old daughter. I love them both and have recently found it hard trying to convey my concern about boundries I feel are being crossed by the 15 year old daughter.

About 2 months ago, upon moving in with my girlfriend and her daughter, I explained to both of them I have no issues doing everyone's laundry, but would truly appreciate if the daughter could separate her under clothes from the rest of her laundry for either her, or her mother to wash. Being new to the home, I found it as more of a respect concern and I have always seen it better for the mom, or daughter to wash a teen daughters cloths. Becoming a women can sometimes get overwhelming and I feel a bit uncomfortable with it to be truthful.
Everyone said ok, there was no more brought up about it, but she has continued to do her own laundry. About 2-3 weeks ago, the 15 year old daughter come walking downstairs wearing only a bra on her upper body and fully clothed otherwise. I immediately asked her mother to address this. I was very embarrassed to say the least. Her mother told me she talked to her, but a week or so later, the daughter does the same thing, but only in a towel this time. Obviously just getting out of the shower, I once again addressed this with her mother and she assured me she would talk to her. Well, this morning, a breaker blew, power went out and the daughter starts walking around the house in just a towel again. I know I handled it wrong, but told my girlfriend she needs to do something about her daughters continued inappropriate attire in my company. I find it embarrassing and more important, highly inappropriate for her to do this.

So, my girlfriend tells me the compromise is buying her a robe. I agreed as long as it didn't become a fashion show and was knee length, perfect. However, she did agree with the daughter as it being new and she shouldn't have to change. So, she would put under clothes on under the towel and they both found this as fair compromise until they buy a robe. I however, DO NOT! My girlfriend says it's just like a Bikini and I said then why bother waste your money on one, just let her where a bra and underwear to the beach.

Sorry, am I wrong here? I find this highly inappropriate and I'm having a hard time understanding how my girlfriend finds it ok? I could agree if it was new, but she has been talked to twice before about this, so she was told not to do it. However, now the mom, my girlfriend, is back tracking, saying her daughter has a point and it's my problem if I'm uncomfortable. I was told to stay in my bedroom if I'm that uncomfortable. Their getting a robe, but until then a towel with under cloths is fine and I need to deal with it. Please help!!!