I have never done anything like this before - but feel like I need somewhere to turn. I am a 24 year old woman without any experience with this whole parenting thing.

First, I need to say that I have the most incredible fiancé. He is sweet, affectionate, loving, and always tries to make me feel better in every situation.

His ex-wife is nuts. She inserts herself into every aspect of our lives. She called him constantly, makes all the decisions for the kids - without any feedback from my fiancé, speaks with his parents and family on a regular basis (calls or stops by their house), and has absolutely no reality of any boundaries. My fiancé is a great person and tries to be a great father to his three girls (two of which are hers). She is constantly coming up with excuses for why the girls can't come to our house. Signing them up for 3-4 sports in any given season and insists on picking them up and taking them to all events. She is constantly putting him (and me) down in front of her children and speaking to them like they are adults who are able to carry on a demeaning conversation - they are 8 and 9 years old.

Luckily, we have made the decision to sell the house that was once theirs. This has been a tedious process, but I was hoping that it would be a means to an end. Unfortunately, this weekend, my fiancé and I had a disagreement. She called on Saturday morning insisting to come to the house to go through old pictures and school papers from when the girls were younger. He knew I would not want her around, as we were busy packing and I get very uncomfortable when she is around. He tried to tell her it was not a good time, only to have her threaten to call for a police escort in order to get into "her" house - which he and I have lived in for 3 years. To make a long story short - she showed up ready for a fight. I was so upset. I had been trying to sell furniture that he and I did not want to bring to our new house. When she found out, she through a fit and insisted that she wanted the pieces. As far as I was concerned, all of those things were over with. She had no right to anything after such time had passed and he did not need to give in to her. My fiancé is one of the nicest people I have met. He wants to keep the peace. Him and I got into an argument later that evening, where his key point was that he would do anything to help his kids. I agree with this 100% - but does giving his ex-wife a dresser really mean he is helping the kids?

On a separate note, I get along with the 15 year old daughter (not his ex-wife's child) beautifully. Her and I are best friends. I also get along very well with his youngest daughter, who is carefree and a breath of fresh air. It is his middle daughter (her oldest) who I can't seem to get along with. This child is good at everything under the sun. She is bright and she knows it. She is continuously involved in sporting activities and never has a moment of down time. Whenever she is with us, she is texting her mother (they both got cell phones two Christmas' ago). I will ask her to do simple things like clean her room or eat dinner before we have dessert - all of which she will run to her mother and say I am being mean to her. She is extremely disrespectful to me (behind closed doors) and will never listen to anything I have to say. She has also started treating her father with the same type of disrespect. She is a sensitive kid, who is still having trouble with the divorce, but it is a constant strain on me and my emotions. It makes me so sad that because her mother does everything but wipe her after she uses the rest room, I am unable to have a relationship with her. Her mother is so easy on her and treats her like a teenager - watching rated R movies, talking about inappropriate topics, listening to very questionable music. Don't get me wrong - I like rap and movies like Knocked-Up, but I feel like I am the only one fighting for her childhood.

My fiancé and I only ever fight about his middle daughter or his ex-wife. Other than those two topics, our relationship is great. He tries so much to keep the peace, but he is constantly giving into his ex-wife or his middle daughter. I feel that he will start to blame me for trying to teach her the only way that I know best - by example. How do I let myself let go of his past (ex-wife) so that doesn't plague me the way that it has been for the last few years? How do I help get someone to understand that his daughter will not become a better person if nobody puts restrictions in her life and let her do anything she wants to do?

I hope I can find a way to at least ease my stress level in these situations. I love my fiancé more than anything in the world and would do anything to make this situation better for all who are involved.