<human>: My girlfriend and I have been dating for almost two years now. Our relationship is great. However, my girlfriend has an unofficially adopted sister (we'll call AS) my same age. Her family took her in when she was 15 (I think) and my girlfriend was 18.

AS is trash. She steals from the family that gave her a home. She steals from my girlfriend. She also has a one year old child from a deadbeat dad (drug dealer, arrested multiple times, etc) and is currently pregnant again with another of his kids.

I hate this girl. She was abused as a kid and talks about how "He'll (her 1YO son) get beat if he does X, Y, or Z." She's always at my girlfriend's house when we visit. Luckily, my girlfriend lives in an apartment so I don't have to deal with AS very often.

My girlfriend's family (mostly her mom) are pushovers about it. They know she's stealing, but haven't done anything or said anything. They still help take care of the kid and give her rides to and from town.

I absolutely hate her kid too. I know he's only 1, but she lets him go wherever. Playing a board game on the floor? He'll crawl onto it, slobber on it, and push everything around. "Oh haha he's just wantin' to play!"

I can't stand it. She's rude, a thief, and lets her kid slobber over anything like a St. Bernard.

I have to go spend a couple hours with them on thanksgiving and I'm going to fucking hate it. I love my girlfriend more than everything, but her adopted sister is a piece of shit. Watching her family get stepped on like this is frustrating. I want them to do something about it but I'm in no position to do or say anything about it.

Does anyone have some advice on how to deal with this?

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: gf's adopted sister steals from family; family knows and does nothing. Also, kid drools on everything around because she doesn't watch it.