This is an excellent thread....very uplifting. I'm downright jealous, Kate, over the availability to you of that bike co-op. That sounds like a dream come true.
I'm approaching the weight issue from the opposite direction; I tend toward skinniness. I also feel a bit embarrassed, sometimes, over my appearance. Even though it's hardly all that bad; I'm recognized as a guy who's in good shape.
Don't forget that the idiots are really pretty rare. Most people will actually approve. I know as fact that most people when seeing an overweight person biking/jogging, etc., will think "Good for her/him". Polite people don't say it, at least to stranger, for fear of seeming rude. But most passersby will have some degree of admiration for you.
Your loved ones may try to dissuade you on the grounds that it's "dangerous". But whether they know it or not, they are really afraid that the world will look down on you. All you can do is forgive them and ignore them. They are looking at it from the wrong end of the telescope, just as you and I have done.
You're a really cute girl. I'm certain that you have more realistic worries than your appearance. You should forget all about that.
It's nice to be associated with a community that is this supportive.
Now ride, ride and ride some more!