If she is in the new grade, then that grade is her actual (real) grade. Maybe it's not the grade that other pupils her age are in, but she is not in any other grade.
I would say something like "she's two grades above the usual grade for her age." I know that's longer, but there's no good short way to say this. One might say her normal grade, but that means that she is abnormal - which is a negative term in this context. I don't like any other word I can think of, either,
I would like to say that this usage of "grade" does not exist in BrE. This may well not matter for you, but we would use "year": "She jumped two years in school". Your scenario is very unlikely in Britain, where skipping years is extremely rare, but I think you could use "two years above her actual year".
If you are only interested in American usage, please ignore this post.