The issue we had was that the high school AP teachers prepared the kids to make a 3 on the exam, but we were shooting for a 5. So far, DS has made 5s on all his APs (STEM heavy) and we purchased the Princeton book for all of them, except AP WH as the teacher was excellent.

Maybe you can get the book and have your DD do it at home and you can somewhat help her schedule it out. Sorry, no help on websites/apps but good luck!