What year in high school is she? What math is she taking, is she in Honors or AP English?
First of all, a 1200 is not a bad score.
It is well above average.
If you want her to have a 1400 score, that might be possible, or it might not.
There are practice tests on the Collegeboard website she can download and print, they are free.
Have her take one under timed conditions like a real test, and see which questions she got wrong.
She might have had a time issue and didn’t finish parts of the test.
She can then do a few more practice tests and see how it goes.
I agree March might be too soon to take an official SAT.
She could take it in May or June, and then in August maybe if she is a junior.