My route is usually use fire until she starts to run away, and follow that up with shotgun shots. It gives you time to reload weapons and you get quite a bit of damage off. Along with this, she rarely has a window to attack you. My boss fight was around a minute with this strategy, but it has a long of RNG elements to it.
Does anyone know if she has Invulnerable Frames? it just seems that if you really lay into her after the 1st or 2nd shot nothing really happens. You have all no doubt done a lot more testing then I have.
I believe the only invincibility frames are when she is crawling out the window, but I think she still takes some damage as long as she is inside the building. The thing is, you can't kill her unless she is on the ground and in the building, so it might just queue up the damage and waits till she drops down. I don't think you can kill her outside of the ground, but it probably will drop her to like 1HP
