The best strat you can do would be to stay in the first room right before you enter into the "Chamber of Omnigul" as I like to call it. Take down her shields with a good arc fusion rifle (Murmur, Plan C work great) then unload on her. As far as enemies go, pick them off from that room and when they are all gone then rush Omnigul. The enemies will spawn when she does her scream (which is terrifying btw) 10-15 minutes if everything goes well. Also homing rockets are amazing with this. Gjallarhon is phenomenal if you have it.