I’m concerned by my gf actions

Both my gf and I are 28 years old and we live in a country where you can legally drink alcohol at 18.

We’ve been together for a month but I just found out something that deeply concerns me. My gf has a girl best friend who is 18 years old. I really don’t understand how she can have things in common with someone who is still a child and can perfectly be on hs!!

This girl is turning 19 next week and as a birthday present she asked to get drunk. Not only drunk but wasted enough she can’t recall what happened on her birthday. And my gf and her male best friend (also 28) are planning a gathering with other friends with the mere goal to get this girl and the guests drunk.

I’m seriously thinking on breaking up with her over this. Why does a teen have to get drunk around a bunch of 25+ people? I spoke with her and she said, that she preferred that her best friend got drunk under her watch than in a bar or disco.

What are your thoughts?

Summary: my f28 gf is planning a to get her best friend f18 drunk for her birthday.