Is it normal that i hate my boyfriend's brother's girl friend?

Ok let me explain this further. I have been dating my boyfriend for almost 4 years. His younger brother has casually dated many girls, and they all come & go. They all have never bothered me. Until this recent one.

First thing that bothered me is how disrespectful she was in front of everyone, including his family. She would cuss a lot like she was talking to her friends & even talks ugly to the brother, like tells him to "Shut the fuck up," in front of his friends. She left her moms house after she graduated high school (I'm assuming she didn't want any rules), and she started staying at a friends house. She would use my boyfriend's brother for rides to work, parties, or wherever she wanted. Eventually the friend she was living with was moving & wanted the girl friend to leave. The girl friend then asks my boyfriends mom if she can move in. My boyfriends mom said no. So next thing we know, she gets pregnant. Mind you, this is literally just one MONTH that they have been together. As soon as she finds out she's pregnant, she MOVES IN. She completely acts at home, walks around naked in a towel after a shower. YES it bothers me, because MY boyfriend is there.

She now tries to treat me like I am the outsider. I have taken a step back honestly, & still try to act like she doesn't exist just to avoid me wanting to kick her ass. Of course the brother & her fight sometimes & she left to stay at her moms one night, my boyfriend who worked overnight that night, comes home to see his front yard destroyed. She tore down all their Christmas lights, threw stuff around, put a car seat box in the front yard, and a filthy one on their door step. My boyfriend was really mad, but what happens? She is there at the house the very next day & the parents act like nothing happened. I called it from day one that she was no good & my boyfriend started to believe me after that. I then had their little sister on my side too, who would tell me how much the girl friend picked on her. She would call her a little baby & make her get her stuff when it was just in the next room. Tell her she needs to do more around the house. While the girl friend just sits on her ass & has the boyfriends mom clean their room. It is just so ridicules. Another thing as if i haven't included enough, She thinks it's okay to NAP in my boyfriends bed, the parent have even let her drive my boyfriends car because "SHE has a license" & the brother doesn't. She'll leave stuff in his room, like her straightener. To piss me off more I am sure. & Also has told the brother in front of his family, that why can't he be more like his brother ! (MY BOYFRIEND)

There is just SO much more she has done that would take forever to write, but is it normal that I hate her for all this? I know she can wish all she wants if she wants my boyfriend. WE are really happy together & I do what I can to not let her phase me! I get along with all the girl friends in the family, but WOW did this girl just shove her way in. What can I do? It's VERY hard to tolerate her. Idk what the hell the parents problem is, but they seem to fail to see the whole picture & practically place her at the same level as me. It offends me sometimes, because I've been working at the same place for years, come from a great family, & go to college. Refuse to trap their son with a baby, and want to do things the right way & leave a good example for his & my little sister. It's just really annoying that his parents don't see that.