I did a lot of work with DS in the early days with short cutting computation- we broke things up into manageable parts, we did a lot of mental math on car rides, we checked out the Sir Cumference book on how to organize to accurately count large numbers. The main "gist" was mental organization to compute quickly. I was a budget manager for years, so learned some skills (for most people, it is a skill) with quick calculations.
It does sound like she may need some help with "math facts" and tips for quick calculations. For instance, once I was sure that my son understood multiplication and struggled through a good deal of mutiplying on his fingers and counting groups on paper, I did successfully use flash cards and the iPad to facilitate memorizing the table (same with division).
Sometimes it takes a bit for things to click- I was like that as a kid with math- not always quick but when I got it, I got it better than most.
