I've noticed several things with Mirri. I have her as a healer so she stays ranged.
---- First, when I am not in combat and am trying to loot a body or cabinet or something my companion is right on my tail. Since I play in far 3rd person POV her position overrides the loot containers position on my reticle and I have to move to clear her from it. Solution, have Mirri and the other companion stay at about 3 persons away on the back right. Have the quest NPC stay on the back left same distance, since they too like to go up to my tail.
---- Next, when in combat Mirri immediately tries to go backward, thus placing her farther and farther from my toon. As a healer she has the healing fountain skill and that has a radius of 28 meters. This often is placed at the far edge or past my position so I never see its synergy. Solution: have healer Mirri stay at 15 meters from combat toon until the toon is stationary for 2 seconds ( stays in one 5 meter area during combat) Then have Mirri run to the side rather than backward, a side that has fewer mobs. Keep her ranged between 15 and 28 meters when a healer or destro staffed. If you could program ground height awareness, have her go up on a short cliff to avoid ground fire and other moving ground attacks from mobs.
---- Last, the bug I see is as a healer her resto staff can taunt off mobs from my group. I attack a mob group and she begins to attack with resto staff light attacks. I should have soft taunt, yet the mobs she is attacking leaves me and goes to her to attack her. I play healer allot and I have never had mobs leave the tank/dps group to attack me if they have been soft taunted. This is a bug.

Thank you