For that specific fight, things like Mamoswine, Excadrill and Camerupt will obviously be the big useful. Steath rocks will also do 25% to most of her team
as for general mons, I think Sandile should currently be available, and Krook has good stats, really nice natural moveset and good abilities for either sweeping or playing more defensively in Moxie and Intimidate.
Flygon can be a powerful sweeper now that it gets dragon dance via move relearner as of gen 7, definitely recommend. but not for the ice gym lol.
Hippowdon with Sand Stream (and smooth rock) is probably really nice for mono ground, and I know it makes excadrill a deadly sweeper, especially with a swords dance (which he gets at 42, so you should be able to relearn that). I don't know when hippopotas is available though, its probably kinda late because I think most weather setters are, and the other sand stream mons are rock only. (actually, looks like they're in Tanzan depths (steelix area) so not too far away? )