The phrase "a hill to die on" means the thing you want to argue about without end. You would often hear it in the phrase "Is that really the hill you want to die on?" meaning "Is that really the point you want to argue?" in the context of someone continually arguing for a point that either no one cares about or is not worth arguing about. In this case, the woman means that it is not worth arguing with people who say that non-indigenous people shouldn't dress up as indigenous people. It's not "a hill to die on" it's not "worth the incessant argument." She says that it's worth giving up on any argument against that, in order to have better race relations. Please let me know if you have any other questions.

It means something that is worth arguing for. So in this case she is saying that one shouldn't argue on a child's Halloween costume as it's not worth the trouble.

to me it sounds like she is talking about an alter...but I speak American English and BBC is British English.

to me it sounds like she is talking about an alter...but I speak American English and BBC is British English.