Hi Bonnie,
I think most of us have, at one point or another, had someone directly or indirectly say something inappropriate about weight, race, gender, etc... Since you have to be around this woman all the time, you kind of only have two choices: say something about it or let it roll off your back. We cannot really control someone else's behavior, but we CAN control our response. I can really understand how difficult it must be to be around her. You might try to say something like: "wow, Mrs. so and so, what you said right now is very hurtful and you seem like a very nice lady." Maybe that would get her to realize that she's very unkind. If that doesn't work, you could say, "I don't really appreciate the way you're talking down to me and I would really like you to stop. I'm here to help, but I'm not here to be insulted." If that doesn't work, then maybe you could let the boss know?
If you decide to take the route of not saying anything, I would suggest just telling yourself that this is a woman who isn't in her right mind. If you found out that she has a brain tumor that affects her personality, that would certainly help you understand her inappropriate comments, right? Well, I think she's just not in her right mind if she thinks that treating people this way is acceptable.
Either way, please don't let this change your outlook on food for the worst. I have a horrible addiction to food and I have learned to separate (for the time being anyway) my food from my emotions. For example, today, my son (who has a disability) had a huge problem at school and I had to come and pick him up and spent quite a few hours feeling sorry for myself and crying my eyes out. Normally, I would have turned to food for comfort, but today, it wasn't an option. Bingeing on food will not make my son better or the situation better. Same thing here. Just remind yourself that eating more will not make you any healthier and who really cares what this lady thinks? If she was a kind human, then you could care about what she thinks, but she's not and so she doesn't deserve your caring about her opinions. Just be there to do your job and know that you are kind and that you are doing the right thing. She'll have to deal with what's coming to her on the other side!