"It would be one thing if she were genuinely up against a limitation in performance... but it isn't. She's missing kind of random stuff, and it's the kind of thing where I can look at it and go.. HUH?? That's a sloppy computational error, or one of "whooops... guess I should have written that formula out rather than pulling it out of my backside on the fly..."
OMG. OMG. OMG. Someone-- please-- talk me down. Tell me what in heck to SAY to her. PLEASE. Because at this point, her behavior is going to make a difference not only in WHERE she eventually goes to college, but also in how much $$$$ we end up shelling out for it. Like it or not, we are not wealthy, and a difference of 10-30K is a kind of big deal to us (which is about what it adds up to at one of her top-choice local private options, over the course of four years)."
I got the semi-thingy and I love making random PSAT/SAT errors. I'm an expert at sloppy math. Speed over accuracy, that's my motto.
Only once did I ever get an 800 on the math section of anything, and that was some achievement test thing.
Although it sounds like she may be being a 13 year old, so the problem may be that she's 13.
I'm certain that I am completely unhelpful here.
The best I can think of is that you need to tell her that the more she does practice tests the higher her score will get and eventually she will get so good at it that she will feel like she's sandblasting a soup cracker. Or a hot knife through butter. I'm getting hungry for some ice cream. With hot fudge. Mmmmmm. Although you use hot spoons to scoop out ice cream, not hot knives. I'm hungry.
And that's how high-stakes standardized tests work.
Not the ice cream, the practice testing.
