If it makes you feel any better, most women treat these nights out as a big laugh. (curbing my own point here because this is your mother we’re talking about but you can read between the lines).

Nobody will judge you for your adult parent going to an adult night out. If any of your pals give you a hard time, crack a few jokes, roll with it and it will pass.

well she’s an adult you can’t tell her what she can or cannot do but you can express you disappointment to her and your feelings about the situation and why you feel this way personally I think it lacks of class , hope things work out for you !