Beaver Canoe is right. Time for play dates with her friends from school, or from her other activities if she has them. If she doesn't -- maybe she needs some activities. I say this all the time on here: Neighborhood "friends" are OK and can become deeper friends, but mostly, lasting friendships come out of shared interests and shared experiences, to me, and not just out of the proximity of living near each other. If there are girls you know your daughter talks about from school, get in touch with their parents and start having play dates.
At these ages (of all three girls involved) there can be a pretty big gap in maturity and interests and social skills among girls. A third grader who's 9 may indeed see your sometimes teary and emotional second grader, still half a year from eight, as too young to be interesting. Those age differences are nothing to an adult or even an older kid, but to early elementary kids -- especially ones who are just, by personality, "older" acting, like the one girl you describe -- these small age differences do create big gaps.
Yes, the other girls are rude and wrong to whisper in front of your child as they do, to leave her in the dust (I'll wager they know perfectly well she can't keep up) and so on. Not nice. It's fine to tell your daughter that it's not nice, but add that real friends do not act that way, and it is perfectly fine if she just turns around and leaves when they do that.
Some parents carp about play dates, setting them up, having to be in touch with other parents about them, etc. as if they're a huge hassle, but I hope you won't go there. It is not micromanaging to start having some play dates with school or activity friends. Many kids are so excited if a parent says, "Ask Sally from school to come over here and play." And yes, you have to make that happen for a long while to come since your child is quite a few years away from calling friends on her own and setting it up--you still have to be chauffeur, check with friends' parents on schedules, etc. Nothing wrong with that. And nothing wrong with bowing out of the neighborhood thing if it is making your kid unhappy -- she is truly not obliged to get out there and "work it out yourself" when the others are not amenable and see nothing to work out. They're tight. She's not, but wants to be. There isn't a friendship here to "work out," which your daughter won't see at first, but you just keep steering her more toward real friends she likes from the rest of her life.
The carpooling aspect makes things a bit tougher. If you really must carpool with Amelia, fine, and that's where your daughter will learn to deal with it better. But she won't care as much if she's got the previous weekend's play date to talk about with you while you're driving them to school.