In our district, January of 3rd grade is when kids start taking timed multiplication tests. Prior to that (Everyday Math, so since 1st grade) they have worked on arrays and the concept of multiplication. Some of the things that are more obscure but might come up as "holes" are a.m. vs. p.m. and elapsed time.
Honestly, though, when my kids accelerated, these tiny "holes" were the only thing that challenged my kids. And challenged is a strong word. The holes were filled almost instantaneously, sometimes with a little practice (which is, afterall, what most kids get), but usually with just a brief discussion of the topic. You'll probably get some concern from teachers and administrators about these holes, but anyone with experience with gifted learners will tell you that holes will not be a problem.
Your main clue to the areas she will need to learn will be what she missed on the end-of-third test she took. You may find, however, that her mere exposure to the questions allowed her to pick up the concepts. Besides, it she is entering into 3rd grade math, they should teach her the concepts she missed on the end-of-third test, just like they will teach all the other 3rd grade students.
