I've been stuck on Bertha for god knows how long and the none of my Pokemon know an ice type move or a water type move (aside from a level 17 bibarel).
Keep beating Aaron until your Pokemon are high-level enough to beat Bertha.
If you can try to get glalie, froslas, abomasnow or a steelix with ice fang and curse as of steelix being slow and having good Defense making it purfect for curse (lowered speed with raised attack and Defense) and if you want to you can add fire and thunder fang to make it just about indestructible also give a wide lens it puts the fangs up to 100 accuracy. If not just teach the other 3 the move ice shard to deal with gliscors speed.
Hope I helped :)