Surely you could blame it on your mom. But it was not your mom, or you. It was her.
Ultimately it was her who decided to "honor" some stupid bullshit promise. She is an adult.
If the love of my life shows up, and her parents say "promise us you will never date her," and she says "but I love you!" FUCK THE PARENTS. I'm marrying that woman. She didn't say "fuck Cheradenine's mom," welp, that's on her.
Plus you did the right thing with the drunken part. I've been in your position. I don't take advantage of impaired people.