AOPS is of course the gold standard if you want a deep grasp of the subject. However, there is no 7th or 8th grade math per se. It starts with Pre-Algebra.
I am also not sure what 7th and 8th grade math include these days. At our school, the top third take Algebra in 7th and at least another third take Algebra in 8th while the bottom third take a course that at least introduces some Algebra topics in 8th.
If you are looking for some superficial coverage of standard topics, ALEKS may be a good bet. It is very cheap/flexible (low monthly charge) and provides Common Core versions as well as skill mastery required for each state. I can't vouch for their 7th and 8th grade math but DS completed Pre-Algebra independently over the course of a few weeks five years ago to verify that acceleration to Pre-Algebra would be warranted. In ALEKS, you go from 6th grade math to either 7th grade math or Pre-Algebra. You don't really need a tutor for ALEKS, particularly for older kids (DS was a couple of years younger than your DD at the time).
Last edited by Quantum2003; 06/20/16 11:01 AM.