What did you use for offerings and what was the battle strategy?
if I remember correctly I had: frost thorns, frost egg, frost blanket, frost golem, a volt projectile, and healing seed.
I just let them notice me and ran to the first arena. I kept ones attention to lead her there. when she was closing in I drop a blanket, use thorns until she was frozen, summon golem, break her out, drop blanket, freeze her, break her out again. the rest of the fight was just me taking shots where I could. she gives a bit of time for you to attack after most of her attacks, and when those times came I used the ice egg. took her down and found the other to do as close to the same as I possibly could, but this time I also used my black rite. also early on when she's in chase mode dropping a blanket and making her run through it a few times usually results in frozen hell.
playing that alone helps to see/remember some openings better. you always need to know when the best time is to get a couple shots off and refill offerings off a minion. after i dodge her volt attack i can get a few shots off. before i would run randomly when she did the tentacle move, but now I usually run towards her to get a few hits up close or drop a blanket for a few seconds. a lot of the problems that arise in multiplayer are from groups splitting up. getting hit by tentacles or the petrify move from across the map is no fun. honestly I think it's my favorite mission because it's always a challenge. the few times I hopped online with randoms it has been to help with this mission.