When Native American fans confronted her about it, she...blocked them. And is still blocking anyone that mentions the costume to her:
@becbecbobec you have native fans like me who are rly disappointed in this. Do you even know what's happening in Indian country right now?— charli with an i (@charlifoolbear) November 1, 2016
:(((( this makes me rly sad! pic.twitter.com/LtEZa7dOA4— charli with an i (@charlifoolbear) November 1, 2016
ETA: She apparently had the foresight to know that the costume was racist and her excuse was that her fiancé is NA.
Sources - 1 2 3 4 5 6 (Now deleted.)