I totally understand where you're coming from. I've been out with gingers in the past so it doesn't bother ME, but I understand that it has that for other people. I'd hate for Myles to turn ginger - not because I wouldn't like it, but because of how he would be treated. Another thing to consider is (as least for ones I've known) gingers tend to be quite outgoing etc. probably because they have to be to overcome how people react to them. This is for boys though, and in my experience it isn't the same for girls.
All I could suggest if it does turn that way, is to make her very happy with her hair colour and have replies for her to say to people that are horrible. Maybe make her aware of other redheads who are famous/have done very well for themselves so that if anyone says something, she can be like "well what about so and so, they're rich, famous, beautiful" etc.
I hope for YOUR sake that she isn't, just because it does seem to be something that would really get to you, but personally I think that little redheads, especially girls, are absolutely gorgeous!