Sorry bud, your girlfriend is an idealist who is on the losing end of the 'culture war'. The fact that she values cultural artifacts over human lives means that she has already accepted defeat, as humans who are alive can always make more cultural artifacts, therefore their lives and causes always take presidence. Isis was bad because they were commiting religious terrorism against the people, not because they were blowing up Persian monuments (although historically that sucks too). Fighting to preserve the past is an academics game, not one of an activist who believes in the future.

As for the tibetans (not nepalese). There was no 'cultural genocide', there was a protracted civil war between the tibetan monarchists and the tibetan maoists, in which the maoists ended up making a deal to bring China in on their side and advocate for annexation (as it makes more sense economically to be connected with a country with a coast line than be landlocked and impoverished). Equating it to the actual genocide and shuffling of the Native Americans done by the U.S. is a gross misinterpretation of both histories. China often does have shitty foreign policy, often supporting stronger conservative factions over weaker, more strictly maoist ones, but the annexation of Tibet is arguably one of the few things they did that was good and was revolutionary correct, and the poverty reduction that has occured in Tibet as a result is a testament to that correct choice.