My girlfriend lets her daughter have the rule of the house. Bed time is sometimes midnight. Any advice? Help!?

My name is Mandie and I have been in a relationship with a woman for just over 2 years now and I love her dearly. She has a seven year old daughter who used to be a nice, soft spoken kid who listened most of the time and wasn't so out of control until she turned 6... After she turned 6, her attitude went downhill at a rapid pace. A number of family members and friends who have witnessed the same attitude and who have babysat, confide in me about her daughters attitude and tell me "I don't know how you do it"... I question myself sometimes also, but I love my girlfriend and I have to stay with her for that reason. One time we went out to eat with a few other couples and we were all sitting at the table and her daughter was acting out so bad it was sickening.. Everyone at the table looked at me, rolled their eyes and shook their heads in shock. The thing that’s even more shocking is that my girlfriend laughs it off and thinks it’s FUNNY that she’s so mouthy!! I have asked my girlfriend a number of times why she allows her daughter to act this way or why she allows her to stay up till whenever we go to bed which is midnight or later on a school night and her answer is always " I don't want to put up a fight every night for her to go to bed or do whatever. I try not to sweat the small things like that. I don't want my daughter to always think I’m angry at her all the time." Can you tell me, does that make sense? This isn’t sweating the small stuff! It’s called discipline and kids need it if you want them to grow up well developed and well mannered. I mean the kid gets everything and I mean everything she wants and my girlfriend still tolerates the kids’ behavior and NEVER sticks to ultimatums because she tells me she feels bad and doesn’t like to drag an argument out. Again, its not “dragging the argument out” it’s DISCIPLINE! Any parent will well mannered kids knows that you need to let the kid suffer the consequences and then learn from their mistakes not to do it again. I've talked to her family and friends and they totally agree with me but since my girlfriend is strongly opinionated and is quite defensive when confronted with parenting topics, even her sister who is closest to her doesn't know what advice to give me on approaching her without an argument. By the way, I hardly confront the family and friends about it, they bring it up to me just as much! My girlfriend just must not see it. My girlfriend and I hardly have any quality alone time together cause she's a single mom and the dad isn’t involved at all, so that means no free weekends or anything like that, so the evening time is the only real time we would get to spend time alone together, like most adults who work the same sort of 9-5 schedule, but her daughter is ALWAYS around cause she lets her have the rule of the house 24/7 literally! Her daughter even makes her feel terrible about the one night every 3 weeks or so we get to go out alone together. She makes such a big deal out of it and I’m not kidding, actually makes the “sad puppy face” to get her way. My girlfriend and I were supposed to go away to a sunny destination for a weekend alone together for the first time in more than a year, but her daughter manipulated her way into coming THE NIGHT BEFORE WE LEFT…. I feel so trapped because I refuse to leave my girlfriend because of my frustration with her daughter but I need help on dealing with these discipline issues and also advice on how to approach her on this stuff without seeming to aggressive or whatnot. To Start, can anyone help me figure out how to make her enforce the 9:00 bed time like every other kid has? I want to start with this because this is something that happens every day and would make a huge positive difference in my day to day life… our lives I guess… Any advice would be great really, I feel so angry all the time. Please help.