Ok, I had the *worst* time with this until I did the following
After like a dozen tries I went ahead to Nar Shaddaa and got some equipt from intro quests there since I was lvl 21-22 anyway, bought Khem a vibroblade out of the Promenade there that was better, also grinded (ground? ha) on space missions to get enough creds for stims and medpacs.
Then, I respec'ed to Darkness only b/c that was the spec of a fellow Sin who had an easy time. also - !!!Put the "Guard" skill on Khem Val!!!
Got all the way up to lvl 23 that way, which I'm not sure was necessary, but after the Darkness respec I was able to beat her the first time and Khem didn't even die.
Guard on Khem helps a *lot*
...I'm not really sure it's the boss anymore that needs tweaking, but maybe the Deception and Madness skill trees. FWIW.
Respec is cheap so if you are set on your spec just redo it after the fight
Best - Valk