Try increasing friendship levels with her. I believe Deimus already answered the question down below. She will pick any one of the following locations from random according to your friendship level with her.
Level 1 - Slimes
Level 2 - Hornet
Level 3 - Jellyfish
Level 4 - Rockspitters
Level 5 - Fire Rays
Level 6 - Dark Fairies, I think. I didn't progress that far yet.
You cannot ask her to go to a specific location yet. (as much as I would want that feature to be implemented, since I end up quickloading the game more times than actually having to autofight because she chose someplace I didn't want her to go )