When is it a problem?

My new gf (18) drinks 3-4x a week and gets drunk. Also comes drunk in the night to sleep with me. Not shitfaced but certainly drunk, strong alc breath, and next day hangover and days following less energy, less happy/bad mood etc. She can drink 4 drinks under an hour, when already being tipsy or on a good level drunk.
She says she doesnt consider it as a problem and normal for her age, and having a gap year.

Im fine with her being young and free, but the worrying part for me is that she stops being responsible towards our relationship. No texting back and when she texts back no consideration for my worries or feeling, saying she goes home (when drunk) and arriving hours later etc. Forgetting parts of her evening, coming home with bruises, When she is sober she understands and sees what it does to me, but yeah its a pattern so shell just have her drinking night out.
Also what bothers me is that i have to enjoy our time together when she is hungover, or less energy, distanced because her mood drops.
Few weeks ago she didnt drink for two weeks and its was a remarkable difference in her state of being and our connection.

So yeah when is it a problem? Besides it being my problem not being able to manage my restlessness or worries that well. I dont lash out on her, am understanding and loving and also being a mirror of her behaviour. I dont demand her to change, but do express that it influences our relationship.