make a 4 point square in the room before the boss, ie:


x1 x2

tank

x3 x4



so that all are in melee range of tank but out of range of each other, they should all be facing towards tank. you should still be able to hit the boss when shes up, and do nothing when she splits. the healer has to be able to individuall heal any one person and spam heals when that person is "targeted" during split phases and even phase1 she targets randomly and does some big dmg to a random person (plus tank).