MIL advice needed

Sorry this is long! My husband and I have been married for almost a year, and together for over 6 years, and I have never been fond of his mother. She has never been unkind to me (to my knowledge) or done anything to mess with our relationship, but it's the kind of person she is that makes me want to avoid her. She is not a person I want to influence my or my children's life. She has 3 sons (one of which is my husband). The middle child has never had his father in his life because she doesn't know who he is. This child is also the most stress inducing child because he is the worst kid I have ever met. He has zero respect for adult authority, has a mouth worse than a sailor, runs away, has not gone to school in almost 3 years, does drugs, the list goes on. And he is only 15 right now. The youngest child does have his father in his life and for that we are thankful because we can tell already he has a better head on his shoulders. But what really irks me is how my husband's mother parents these two boys. (My husband had his father in his life and is nothing like his brothers). To me she is not a parent. Other things that seriously get to me about her is that the entire time my husband and I have been together she has been living in a falling apart cockroach infested trailer. I can't stand being over there. She has cats that keep putting out litters, she smokes in this dump, and she can never keep a job because she doesn't play well with others. All of her money comes from my husband's father, who is well off and is an overly generous person. He pays all of her bills while she does nothing. I can't stand this type of person, it drives me to the edge! I am struggling so much to love her, and I want to find peace with my feelings about her but just when I think I can forget the kind of person she is and show her the love from a child that she really needs something in me just goes off and makes me care less if I ever saw her again. It upsets my husband when I pitch an attitude about her stopping by our house (I try not to but I'm not very good at hiding my emotions) and he gets upset about me not liking his mom because she has never done anything wrong to me. He has a valid argument. 
I'm looking for any advice any of you would have to offer, I want to be able to get over myself and my judgements because she is my MIL.