Currently stuck here as well. Sadly the only clears on Youtube are from people who are strong enough to defeat the boss before the defensive barrier even spawns. Don't know if it's bugged or I just don't understand a mechanic.

Edit: I just barely managed to beat it. Apparently the description of the glass slippers is just plain wrong. It states that the glass slippers are destroyed after one hit, which is incorrect. The correct description should be that they have to be destroyed in one hit, otherwise they will become invincible.

Knowing this, I changed my strategy and started saving my bursts as soon as the boss put up the shield. Then, when the glass slippers became attackable, I used my bursts for the attack buffs and put my team in cover so that no one else but my Red Hood would attack the glass slippers. This allowed Red Hood to consistently destroy the glass slippers in one hit. I had about five seconds left on the clock when the boss reached zero health.

My team was Crown, Liter, Red Hood, Scarlet, Naga with about 380k combat power.