Maybe there is some underlying issue going on and your mom has decided to use it as reason to remark about your hair. That's a stupid reason, but is one nonetheless and if she hasn't had a problem until now, then I think something else is probably going on and she's taking it out on you which isn't fair at all, but good on you for sticking to your resolve. If not a man bun, then a messy bun? My sisters often do this to get hair out of their eyes while working on a project because sometimes the ponytail gets in the way, so if it's up in a bun, it can't. I don't think you need a beard, but you have a nice jaw structure and could probably pull it off, even if there is a difference of color, but you also look just fine as is, so if you don't wish to grow one out, then you don't have to.