<human>: Summarize the given text in a few sentences.

So I've been going out with my girlfriend for around 3 months now. I've been staying over at my girlfriends most weekends since we've been together, and every time I'm there either a Saturday or a Friday night, her mother always drinks, even on the few week day after noons I've dropped my girlfriend off and gone in and her mother is drinking. 

It didn't really appear to bother my girlfriend up until recently. A few hours ago I was over at hers for a while watching movies. We decided we were gonna go for a quick smoke, my girlfriend goes to grab her cigarettes and I followed her.

We in the smoking room with her mother and one of her mothers friends. Her mum started an argument with my girlfriend that the pack she bought belonged to her. She eventually admited it didn't when she was proven wrong. My girlfriend was visibly upset. So she decided she was gonna take the pack and put it in her bag and we were gonna go smoke down the street. As my girlfriend leans over to pick up the pack her mum, gives her a soft spank on her butt and starts playing with it. My gf then proceeds to ask her to stop as it's quite embarasing. At this stage I was fumming, I was so close to punching her mother, so I removed myself from the situation. As I'm down the street her mum came yelling at me cause apparently I didn't greet her.  My girlfriend is trying to stop her. I decided I was just gonna humour her mother and great her like she asked.  

We eventually went back to watching movies after talking about what happend and how she doesn't want to be like her mother. 

I honestly have no idea how to help her and if there is anything I should be doing.
<bot>: staying with my gf, her mum drunkinly starts embarasing her, and I dunno how to help.