She's good anywhere you want lots of troops killed at once, but also can hit many heroes at once, so that's good too.
I used her to get through HBM AG. She was a huge help there, and in ember army. Because of her I reliably beat Hero Trials L18 and often 19. I use her in raiding, even in preference to Dove Keeper. Her tank has good staying power and helps heal her, plus she goes elusive as part of her summons's proc. All three of those things help keep her out of trouble. Meanwhile, she and her summons keep on doing their damage.
Since I find her useful mostly for her summons, I'd suggest a defensive talent for her. I have flameguard and it works very well. Stoneskin would also be good, and I guess I'd put bulwark third place as far as how much it contributes to survivability. If you can get a defensive enchantment and traits on her, I'd do that too. Mine has mostly hitpoint traits and one dodge.