It may be hard, Dog, but maybe you should just ask her to sit down and talk about it seriously.
With an open mind, ask her why she doesn't like the bald head on you. Without getting offended by her answer, explain to her that being shaved bald is viewed completely different by the masses, than it is by her generation. We are not neo-nazis and we don't hate everybody (just an example, not assuming that she thinks we're nazis

) Then give her the reason why you do it, which I know you have before, but it may be better accepted in that moment.
I then would even go as far to telling her that you are part of a supportive community on the internet, and that we all know about the battle you're going through, and we help eachother out when we're seeking that needed confidence. This will hopefully let her realize how much her comments are affecting you.
As hard as it can be, just remember to not come back with any fighting words. It will show maturity, and that you're serious about your decision.
It sounds like a "let's hold hands, everything is groovy" way to go about things, but it may work.
Whatever you choose to do, just remember your relationship with her is bigger than any hairstyle you have, and you'll be just fine in the long run.