Honestly I'm never one to judge someone by their looks. I'm a 23 yr old mom who has a giant fairy tattooed on her back and looping around my hips and multiple piercings myself; so I'm in your ring....lol.
No, I think we are in an age where appearances aren't anything anymore, yet there are still many "old-timers" that frown on someone who isn't in the "norm" of social attire.
Think about it, at the turn of the last century people who had tattoo and piercings were side-show attractions at freak shows, now there are tattoo palors on every corner, its now more accepting. But I think I'm kind of getting off the point.
My point exactly is, that you seem like a nice person; obviously someone judging you by your appearance and not personality isn't giving you a fair chance. Honestly, I would bring this up to her. If I were you I would confront her and question her if she likes you or not. I know this seems extreme but in the end you'll seem like the bigger person because you had guts to bring up something like this. If she says that she doesn't like you because of your appearance then I would tell her that she is in the wrong for judging you by such a silly thing and not seeing the person you are inside. I would ask her if she rather have her son dating someone who has the appearance of an angel but the attitude of a devil.
Just remember to be yourself, don't struggle or go out of your way to prove yourself worthy of her affection. In the end it will all work out; just stay positive and just continue to act kind and polite and be that help sweet person that you are and in the end it will all work out.