Firstly, I have no idea what they mean by Nepalese Cultural genocide. There was one in Bhutan but not in China. Maybe she is thinking of Tibet, in which case the counter arguments are easy?

Secondly, as an art historian, she will be aware that the purpose of most art is the reinforcement of cultural hegemony, the dictatorship of a social class and structure.

Ask her what should be done with art that has oppressive or otherwise negative cultural meaning? Should the Chinese have tolerated the existence of their equivalent of a Jefferson Davis statue? Should the French have kept up the statues of Louis XVI because some guy 300 years later might want to look at them, when Habsburg armies were breathing down their neck?

Perhaps closer to home, point out how she might feel about important western works that, despite having real artistic value are deeply racist to Native Americans (the opera Les Indes Galantes is one I can think of off the top of my head.) Should that still be performed as a historic artifact? Now imagine how Han Chinese and other Chinese peoples might feel about the Manchu dynasty, which was, after all, an occupying force over most of its territory, and then collaborated with the Fascists. Or about the many later warlords, most of whom were not native to the areas they controlled. Or, in the case of Tibet, the artistry and culture used to justify a bloody, horrifying theocracy that whatever mistakes China may have made afterwards, desperately needed to go.