If you are referring to her accepting the cross-over democrat vote, no, that's not cheating. The article reads like the author takes exception to her willingness to deprive a candidacy resulting from a republican primary process because she didn't like the results. I think she is called a cheater because she “cheated” the majority of republicans (as in primary voting republicans)out of their chosen candidate. In effect, we had the republican primary all over again, this time with democrats allowed to vote in it. Thus the cheater referance.
God Help Mitch McConnell if he accepts Murkowski in the Republican caucus! Let her survive as a Democrat.