I don't think a mouse could land on a snake's head hard enough to damage it.
Not saying it couldn't happen... but I doubt it, myself.
I'd think maybe that gas bubble is the culbrit. Your snake sounded like their snake, and if the gas bubble was behind some blockage, then that could have done her in.
I'm so sorry she did not make it, and know that you did everything you could to help her. HUGS.