Just a thought...sometimes the burnt tips arent just a nute burn, i feel like more leaves would be burnt. But occasionally light and heat can burn...i see you have a pretty strong watt light and high 80s, maybe up your humidity, and take your light a couple inches higher to 24 or reduce the hours to an 18/6? I too suffer from low humidity being in the desert and placing a cup over my plants has helped to keep them humidified when the grow area couldn't stay high. I poked a few air holes and then would mist the cup/container a couple times a day.
Best of luck, i think she'll pull through, these plants are a lot tougher than they get credit for. ✌️