I spent 3 Stamina to test something, and after failing it, this is what I learned:
Level Leanne since she can block 3 units.
Leo at level 40 can handle most of the beginning. When the wolves start pouring in, swap to Leanne or your Ninja(her name escapes me).
Leanne could block 3 and hopefully DPS fast enough
Your Ninja can deal decent damage to things and hopefully kill them before they even reach your Ninja.
If none of that works, then your next action should either be Promoting/CC/Class Evolve Katie so she can block 3 units then get her to level 30 or something.
Now, if I had more Stamina, It'd try it again, but that's all I got for now.
-update-
Just tested it with a team that was psudo to your's
I had a level 40 Leo open up, until the wolves popped in
Then I swapped to Leanne and managed to 2 star the mission.
I hope this at least helps you a little...
Level either Leanne for it, or Katie since Soldiers do deal more damage than the heavy armors, but I don't know if it'll be fast enough.