Lorelei is the queen of Ice-types. However, 4 out of 5 of her Pokémon are also Water, so put away those Fire, Rock and Steel-types. That leaves Fighting-types. Plus you’ll probably want Grass and Electric to combat the Water-types.
First up is Dewgong, an evolved Seel. This creature is Water/Ice, so it’s weak to Grass, Electric, Rock and Fighting. It can attack with Waterfall, and can use Aqua Jet and Ice Shard to try and go first. Grass and Rock-types should be cautious because Dewgong is strong against them. Use Electric and Fighting if possible.
Next can be Jynx. It’s weak to Fire, Rock, Bug, Ghost, Dark and Steel. For attacks, you’re looking at STAB Blizzard and Psychic, plus Lovely Kiss to induce Sleep. Jynx is the only Pokémon that you should send a Fire or Rock-type against. However, if you have one, Steel is the best choice by far.
Cloyster is Water/Ice so shares the same weaknesses as Dewgong. For attacks, it has Hydro Pump and Ice Beam for STAB, and Spike Cannon for resistant targets. You may recall Cloyster has awful Special Defense, so even a neutral special attack could probably one-shot it, if the user is strong enough.
Moving on, we have Lapras, Lorelei’s strongest Pokémon. This one is Water/Ice too, so you already know its weaknesses. Lapras can use Hydro Pump and Blizzard, both of which are powerful attacks boosted by STAB. Plus Dragon Pulse. Try to stick with a strong Electric or Fighting-type. A Mega Venusaur can probably outdo it.
Finally, there’s Slowbro that isn’t an Ice-type at all, but Water/Psychic. So it’s weak to Grass, Electric, Bug, Ghost and Dark. This dopey thing can use STAB Surf and Psychic, plus Flamethrower to sizzle Grass-types. Grass-types that aren’t Poison shouldn’t be scared though.