The purple hair is a blatant ignoring of the rules of the Star Wars universe that Lucas has carefully crafted over the course of 35 years.
Think about it. Lucas threw all sorts of weird stuff at us, including spherical space stations, green aliens with horns, 10ft tall slugs, 1000 degree swords and dozens of alien planets, but he never, EVER shoved humans with weird hair colors down our throats.
The Last Jedi payed homage to so many parts of Lucas’ original work, but they completely ruined it by having this one character with a very outstanding characteristic in marked contrast with everything else the series ever had up until then. That was for me the primary reason this character had to go completely. It had nothing to do with her gender, or the fact she didn’t tell Poe the plan (although that was pretty stupid). If she hadn’t had purple hair, I probably would have allowed her to stay in the film with her lightspeed suicide.