Pro-tip - Buy (or steal) her potion of invisibility before you turn on her!
As for the ogres. I gave them a try on one attempt, They spawned in awkward locations. The two melee ones got shredded by the Redcaps and the caster was stuck on a ledge overlooking everything providing somewhat mediocre fire-support.
Same, though I used them for the masked thralls first and then paid the ogres to use the horn again because the meat wasn't enough for em'. But they bugged out in Ethel's room. But, I managed to beat her down by myself just fine. She is intimidating when she has her doubles but you just need to focus down the real Ethel.
After however I could not talk to Maryana because she was stuck on an acid puddle and the ogres were still considered 'in combat' so I had to kill the ogres. But it's okay, you get a nice +int crown from the leader.