My friends daughter hair pullings & I don't know what to do!

I have this mom friend I've known for about 3 years now. She has a 2 year old and a 7 month old. We used to hang out a lot up until recently since I had to move neighborhoods. However, I've been extremely reluctant to see her because her 2 year old daughter is a hair puller. In EVERY interaction she has had with my son, my son's hair has been pulled HARD. My son is 20 months old and he has long brown hair, so I guess the daughter thinks it's fun? Anyway, her hair pulling has gotten progressively worse. My friend is distressed and confided in me that she is slowly pulling herself out of every mom group because her daughter pulls hair to every kid. She explained to me that her daughter P does it for the thrill, reaction and then smiles/laughs as the other child cries. She's at her wits ends. She claims that gentle parenting doesn't work with her, yelling doesn't work with her so they are trying time outs. I saw it in action a couple days ago and I don't think that's working either cause the daughter P is just laughing/giggling. I can see that all of it is a game to her. Something the dad has been doing is pulling P's hair when she's in time out and telling her "do you like it when I pull your hair? No!"

I thought that is excessive cause you're teaching her to pull hair.

I don't know what to do cause:

1. Not my daughter. Not my place to discipline

2. How do I approach them and tell them that pulling her hair might be making the situation worse? Should I even approach them?

3. I don't really want to hang out with them anymore but I fee bad about it. My son doesn't like P. He's very gentle and sweet and every time he sees her he climbs up to me and is hugging me the whole time. Well of course, he knows P can hurt him! I don't want to keep putting my son in a situation he feels unsafe. But I feel bad cause my friend is starting to lose friends and feel lonely.

I just don't think they're approaching the situation well but I don't blame them. They're frustrated that to them nothing seems to work because P pulls her out of impulse now. We saw her two days ago and the minute my son and I sat down on the floor she came up and instantly pulled my son's hair. The parents are constantly on top of her trying to prevent the pulling but she's too fast about it. I feel bad for my friend but I also want this distance for my son's sake.

What do I do? Is it selfish of me to distance myself? Should I even say something??