What might cause a person to have such a strong and unusual reaction to drinking liquor (details)

I am going to try to word this carefully, as I don’t want anyone to feel “outed” by what I’m going to say… but I desperately want to understand how and why this happens.

I have a very good friend who has a strange reaction nearly every time she consumes liquor. I feel like it is important to mention that she has never had an experience like this if she is drinking beer or wine… it only happens if she drinks hard liquor. It also doesn’t appear to take very much drinking for this to happen, either.

First of all, she blacks out. She will have zero recollection of what happened from the point that she blacks out, it’s as if she just went to sleep, no memory of it whatsoever. For those of us who are awake, coherent, and witnessing this… she behaves in a way that I have never seen another human being behave. Typical behavior for a person who is drunk, I suppose, but it’s very exaggerated. She is extremely loud, violent, clumsy and destructive. She becomes very promiscuous and seems to forget any social norms, often fondling strangers, taking off her clothes, or trying to kiss people (though, she is married.)

When this happens, it’s very clear to an observer that she… isn’t aware of what she is doing. I would describe it as though the lights are on but no one is home. There is something about her eyes, it’s as if the real person has left her body, and it has been taken over by a… tornado.

As for any other important details, she doesn’t drink frequently, maybe once a week.. and rarely to the point of being drunk. Again, it doesn’t seem to be that she is drinking too much, because I have seen this happen after one or two drinks, and sometimes it never happens at all… and it only happens with hard liquor. She does not take medication.

Can someone explain to me what is going on or why this happens? In 29 years I have never seen anything else like it.