Sorry, I don't look at the discussion tab much and it doesn't show on notifications - Pinkamena's damage is mostly melee, the fire is very little, but you have to not get hit in melee by the boss at all. You can either kite with archery or while transformed (then you can run as fast), get her minions (and yours) in between so she can't reach, or lure to the giant derpy who will disable. Her melee attack is also very slow and can be dodged if timed right.

i got one its kinda cheating but go into console andclick on her then just type kill...she will die
(ths is only if you are mad or desperate otherwise keep trying!)