I am assuming NFHS, as well.
Just to be clear, was the contact malicious? To use the RB terminology, did the contact involve "excessive force"? If so, the MC supersedes obstruction (8-6-14). Additionally, the timing of the contact is important.
It comes down to your judgment. Did the MC occur before or after she touched the plate? In either case, you have a dead ball as soon as it occurs. If the MC occurred before she touched the plate, she's out and ejected and all other runners return to the last legally touched base at the time of the MC. If it was after she scored, she's ejected and all other runners return.
As for me, the runner loses the benefit of the doubt and she's going to be out unless I'm 110% certain she scored before the MC.