I have tried beating this baddie with a couple different teams, but I can never seem to survive when they summon the little creatures. They decimate my team and I can't figure out why or how to block it. Has anyone had luck beating this enemy/figured out the best strategy?

Your only hope is to quickly destroy the 2 additional enemies before they can start shooting their beams. You have two turns to do it, starting with the turn Kowlla starts summoning them. You should have Training Grounds at Rank 3 and be using the buff from that facility. What I do first is slowly damage Kowlla and block when she first reaches 150 mana. Then, I try to get her to less than 80% hp, while making sure my pets have dps buffs on before that is reached.

I use Light/Fire/Air. Light is for tanking/healing. Fire is for an AoE nuke on the first turn with Conflagrate when Kowlla starts summoning allies; the Air pet is for decimate on the second turn against one of the wisps, while your other two pets should use Finishing Blow against the other wisp. You need to take them both down by this point. If one is left up, it'll do about 90% of your pets' max HP in damage to your entire team and likely kill you. If both are left up, you're done for unless you run away.

After a certain number of turns, about 30-40, Kowlla will repeat the wisp summoning, so try to get her down fast before that happens.