I haven’t chimed in here yet, but have liked several posts. A 520 SAT score and a B are not bad results. And people, no matter how smart or how analytically gifted, do reach a point in math where it suddenly becomes significantly more challenging for them (with some reaching that point earlier than others).
That said, however, the part that gives me pause is that your D was pretty equivalent between verbal and math tests and that now there is a big difference, and you observed that change occurred with virtual instruction. It could be that this is where she would have naturally hit a wall in mathematics instruction, which is totally fine. But due to the circumstances, I think it would be worth delving a little further and having some tutoring to see what her holes are (particularly based on the instruction that was delivered virtually) to see if it’s a shaky foundation or if she’s reached the point where math no longer comes easily to her.
@Blossom’s point about math sense is right on, though. Being able to understand what numbers mean in real terms is essential. If the number goes up, is that good or bad? Or how much weight should we give to result from a survey that has a big margin of error? Or looking at the sample size between surveys to determine which has better credibility? Being able to see what patterns are being formed and what importance that pattern has.
I work in a field where there are plenty of people with Master’s and doctorate degrees, and it still astounds me that when a simple chart or graph is presented with some pretty obvious (to me) information, we still need to write narrative statements to state the obvious as not everyone is getting it, i.e. a school’s test scores dropped for four out of the last five years, but it still outperformed the district’s median.
If she has poor math sense, that is what I think is crucial to be addressed for her life as an adult. Whether she has difficulty with quadratic equations (Algebra I) or differential equations (calculus) is of far less importance; it is highly unlikely to make a difference in her life.