Ok, I reviewed 6 of her games. Whenever I do something like this I choose an equal number of wins and losses, and try to only choose games over 30 moves (and she had plenty).
I'd say her strategic knowledge is very narrow, she has the same 1 or 2 ideas every game... which is normal for new-ish players, that's fine. When the idea happens to be ok she does fine, and in positions where it's not ok she does poorly.
I've seen players like this before get stuck at e.g. 1700 in 10+0 games, so the fact that she's 2000 must mean her tactics are above average (just guessing). Also her time management seemed very good to me (not too fast or too slow) so that might help her too.
So once she expands her strategic knowledge a bit, she'll probably shoot up. That's my analysis... hard to put a number on it since I don't work with USCF players, so IDK.
If she's reading this, this is the pawn structure you're often choosing, particularly as black:
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You have to be really hungry for the e5 or c5 break. e5 is usually preferable if possible since it will also open your light square bishop. By "hungry" I mean sometimes even as a temporary pawn sacrifice... really push the boundary of what seems safe, because if you never get to play either, then you'll just be squished with no space, which is how I saw several losses as black play out.
And this is not my genius idea, this is how these structures are played. In the link below look at both the caro and slav formations, and notice the advice is e5 or c5 in both.
https://en.wikipedia.org/wiki/Pawn_structure#Caro_formation
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On a personal note I dislike how quickly dxc is played in the games, I'd rather setup e5 or c5 when I still have the d pawn... but ok, dxc it's often a move, and maybe that's what you like. That's fine. But afterwards, preferably in the early mid game, you need to find a way to engineer either c5 or e5.
Hmm, interesting, I'll check out her games.
1800 USCF -> 2500 chess.com blitz, sure, some kids are like that, but even for kids it's rare to have such a large gap.
Her account is @smalltowngoose.
As much as I despise the London for players at her level, it does one thing for her: gets her out of the opening in a halfway decent position. Then her focus on tactics is what allows her to do well online.