I would move on. The same topics repeat year after year. Sometimes your brain really does need to "sleep on it." She will use those skills learned in 2A throughout 2B as well. If she is having a problem with those problems you mentions x - 12 = 75 then you could do some fact families drills. I forget what SM calls them but that is what MM calls them. MM has worksheets dedicated to this.
Something like:
10 + 8 = 18
8 + 10 = 18
18 - 10 = 8
18- 8 = 10
And random blanks will be missing. Or give 3 digits and show how you can make 2 addition and 2 subtraction problems. Or you could just focus on THOSE types of problems and do a few per day. Sometimes when we get stuck I will move on, but do one or two like problems per day. You could easily make them up and do it at the beginning or end of math on the white board.