The best strategy is to just not care about strategy. Just mindlessly mash left, right, down, up, and space.
At first, I was just randomly mashing the arrow keys, controlling switches between forms depending on how much health I had, but even that stopped working by the third enemy; often I couldn't get her to heal herself in time, because it would take about 5 seconds of button mashing before I got her to heal. The Heal command seemed to keep changing; at first I could've sworn it was LLRR (in Defense form), and I could reliably execute it several times in a row just by alternately mashing left and right, but after a couple enemies that stopped working. I couldn't get her to heal herself with just left and right any more; I think the combo changed to something that had a Down somewhere in the middle of it.
Eventually, I gave up on strategy altogether. I stopped being selective in which arrows I mashed, because it clearly didn't have much influence over what moves would be performed. And I even started hitting space randomly mid-combo...
I immediately mowed through the rest of the game.