I agree that glav would really mess Gammoth up with a body hit considering the fire element, however if Gammoth used it's tusks or crest to block the hit it may be able to move in and roll glav with sheer mass alone. Hard to say who would come out on top.

That is assuming her tusks and crest are durable enough to withstand the tail blade, though I doubt the tusts would survive a heated tail blade. Not to mention, glavy is capable of spitting fireballs.