Mostima!!! The key to victory was Mostima.
Of course I couldn't let yesterday's defeat slide despite what I've said, so I just had to try again.
So what did I do differently this time? Weeeell, disregarding most of /akg/'s advice of bringing addional healers and the like. Instead I finally pumped all my resources into Mostima. But she's bad without the module, don't bother with her, they said...? Nope! She was dishing out damage against the lower lane enemies like a champ! The flyers didn't have enough time to kill Warfarin and the blue angel killed some heavy enemies as well, thereby taking off pressure from Typhon, who could focus down the truly dangerous enemies instead of the beefy fodder.
And once everything was in place... the boss was easy. Mandy or whatever she's called got her butt kicked. Didn't even have to drop the pillars on her head.
So yeah, lessons learned: follow your heart more often when raising girls with haloes and devil tails! Thanks again for the Typhons and strategizing.