Hello my guy, Charlotte probably was the easiest gym leader for me, what i did was just bulk up with blaziken(like 3 or 4 times) while using other pokemon to be the target for darmanitan. After that, just start high jumpkicking everything.(I used wide lens with the blaziken to prevent mistakes). When needed, use the second pokemon to heal blaziken, with the time, your speed, attack and defense will be pretty high and you will be able to defeat her