I am a fat person, and bless you for asking. I have struggled my entire life. I am doing well now, but I have been in that super morbidly obese category and I have used a scooter when I was not doing well. I knew why I was in that scooter, and maybe it is just sitting down there, but you have probably figured out that we hear those comments, and we know that she intends for us to hear them because otherwise there would be no point in her saying anything; it is not an accidental slippage of her thoughts that just happened to escape her lips; using that wisper tone takes intent. Saying it under her breath, that is a cop out she uses to pretend that she did not hurt another human being. I am sure that you understand that, or it would not bother you that we might think you also think like she does, or that you think that there is any excuse for voicing something that has no other value than to hurt another of God's Children.
If you are a real friend, then be honest with her. Tell her that you are disapointed that such a terrific person does something that is so mean, and that you expect more of her than that. Nothing is worse than having someone you care about be disapointed in you.
You might also tell her that she is really hurting herself. I can fix my issue. There will come a time when she might not be able to fix hers. I heard a homily once from a priest who asked us what would happen to us personally if Christ came again as the kind of person we judged wrongly? What if he hung out with the worst in society? Would we be able to pick him out of a crowd? If this is something you find helpful, you might ask her, what if Christ was walking with the person in the scooter? Would she want to say something "under her breath" then? How would she know? I don't know if that helps you, or if this is relevant, and I don't mean to start any religous debates; I respect all people and thier choices, but this homily resinated wtih me, and I often ask my children this question to get my point into thier heads when they are doing something that they know is nasty but are justifying it for one reason or another.
I hope you can help her. Incedentally, though I am not in a scooter now, and I am fit and eat well, I am not a small person. I am a smaller person, I am healthy, and I am active, but your friend might see me and still comment. We are all worthy. She may not have any idea what a success story looks like...it might still be ugly to her. Please let her know that.
M.
@Mum4ever: Give your son a hug and kiss. What a gem.