If the only score she has is the 10th grade PSAT, definitely link her CollegeBoard account to Khan Academy and have her do one of the practice tests there. Most kids improve and if she is in AP Lang, she probably is actually covering these topics this year.
My son had a 650 on the 10th grade PSAT writing/English, but tested at 700 when he started his (minimal) test prep for the SAT.
I've read good things about the Meltzer books, but my kid was not going to go through hundreds of pages of grammar. He did the Khan Academy exercises and found them helpful.