I've thought about MOOCs. However, part of the equation is that she doesn't find computer interactions as satisfying as meeting people. I think it is part of being 9 and hopefully she will get more comfortable with online interactions as she gets older. Having a chance to talk with people about her interests and work is deeply satisfying to her.
The school isn't likely to be much help. I do have report cards showing her grade levels, but I just don't think people would take that as seriously. The school has a philosophy of independent study, but they are also against acceleration to classes with those of different ages. It's a fluke my daughter was accelerated even a single grade (we moved her to private school and they gave her the skip to get us to send her there, then tried to make her repeat the grade). I don't think they would be supportive.
At the same time, though, my daughter is in no rush to grow up and it almost seems like less pressure to deal with adults than to deal with kids slightly older who are pushing her towards all sorts of preteen and teen things that she doesn't want to deal with (she just tells them she was grade skipped and isn't old enough, but I think that's a convenient thing to say and that she would probably be dealing with the same things even without the grade skip).