Having done this as a healing spec sorc and a tank spec assa I have to say it was alot easier on my sorc. With both chrs I did this at lvl 30, but the main difference being that as a healer Khem was well geared and my main companion. The fight took a while but was one shotted with no issues. Whereas playing this with a tank Andronikas was my main companion and I obtained him a lot earlier that I should have, Khem had been ignored gear wise for a long time. With my tank I died once and had to reset the fight a couple of times when I realised it was going badly. You really cannot just stand toe to toe and expect to win. Get out of the AOE Lightning, make Zash move out of her AOE healing, LOS her with a pillar on her lightning casts. These are all useful things that will reduce the amount she heals herself and damages you. As many peeps have said on here interupts are very important (although with my healer I did not find this to be the case) you will not be able to interupt everything, but you really don't have to. Heroic Moment is also really useful. If you are in an encounter and you feel that it's just not working, try changing things up a bit, failing that ask a friend to help.