If she can understand a decent amount of the math in a 2nd grade workbook, then she's advanced beyond the K math curriculum that our school district teaches.
Regarding assessments, different schools/districts have different assessment tests they use. I'd recommend looking at your school district's elementary math curriculum to compare your daughter's math skills to K, 1st, 2nd, etc. math skills; or if you're in private school, request a summary of year-end skills or a copy of the year-end proficiency test for each grade. That comparison will tell you if your DD is average, or if she really is accelerated.
We did that before we requested the acceleration, and it gave us the information we needed to feel confident in our request. DH and I then listed out DS's math skills and presented them to the K teacher. They did a math assessment and moved him up fairly quickly. If he hadn't passed all of it, they told us they'd do curriculum compaction and then move him to 1st grade math for 2nd semester, so that's another option if for some reason your DD has some gaps. If your K curriculum is similar to ours though, I'm guessing she's not going to have gaps based on your original post.
