Can they fire me for not wearing makeup?

I work at a little family owned restaurant in a very small town. Now I usually wear makeup to work, but the other day, I was in a rush and decided to skip doing my makeup, and just threw my hair up in a bun. So at the end of my shift the owner (who's a woman) sat me down and told me that I need to wear makeup because without it I don't look good, and nobody wants to get their food from someone who doesn't look good. I'm kinda offended because she pretty much told me I look ugly without makeup on. And I shouldn't have to wear makeup to feel pretty. So my next shift I'm not gonna wear makeup.. But I wanna get your ladies opinions!!

And before anyone says anything I do not need this job!! I literally do this for chump change and way to spend my time.

Add: I'm not trying to sue as I don't need the money or anything. Just upset and feel that it was extremely wrong of her to judge me and I don't want her treating other girls this way. My looks have nothing to do with my capabilities to do my job ya know? Another thing I wasn't dirty, my uniform was clean and ironed, I smelt good I just didn't have my make up on , my hair was in a bun but not a messy one a neat one. I feel like I should be judged by the way I do my job not the way I look.