Welcome! smile It is a great relief to find someplace where you can talk and tell all about your child without getting those nasty comments. It was like a weight off my shoulders when I found this a few months ago.
If your child is ready for math and reading then get a few activity books for preschool and see what she does with them. Try it out as a new play thing and if she eats it up (like she probably will) then keep going with it. If she likes it, then there's no reason not to do something she enjoys.
As far as fitting in - we all have issues of that, but I think all kids have some issues with fitting in, or not, at some point in their lives. It's just that ours seem to get to that point more rapidly than others. (as they do with most everything else they do)
As far as your sister goes, my family/friends have made similar type comments and I think there are 2 things going on here: one is actually a verbalization of how difficult it must be for you as a parent of such a unique child, and also perhaps a bit jealousy that their bright kids aren't as bright as yours is. I think this is especially true if there was/is any sibling rivalry going on.
I'm sure she keeps you jumping, but enjoy her talents and go with your gut about how much or how little to "teach" her. We took the philosophy, with our DD6, that if she was ready and willing to learn, then we'd give her the exposure and see what she did with it. We were not pushy about it and if she wasn't interested in something we let it be until she went back to it herself. And it was usually a short time before she went back to whatever it was and got interested in it. (Sometimes a day other times a few months)
I know what you mean about answering those developmental questions too. I think we've all come across them. I use to say I couldn't remember, but I now tell the truth and add a bit at the end that isn't it amazing that all kids grow and learn at such different rates - it makes the world an interesting place, doesn't it? smirk

Welcome again,
Kerry