The 4th Gym actually took me a few tries, I wouldn't take it lightly! What really helps though is if you have any Fire Types that know moves that can set the forest on fire. Her Pokémon that touch the ground (as in, not part Flying or have Levitate) take lots of damage from it in between turns. Personally, I used Slugma with Flame Burst.
I swear the gym was easier than the other three. o.o
I also expected to level a bit more in the battle, so wasted losing four levels on Noibat/Camerupt/Emolga to drop them down 32. >_>
Though I did have these Pokemon on rotation by Gym 4 (bolded is my go-out team rotational ):
Swirlix
Camerupt
Noibat
Fearow *
Emolga *
Trubbish
____
Gothita
Meowistic *
Mightyena *
Grovyle
Klink