Pure stat check. Farm EXP until your units can withstand her attacks. Distribute spawns in corners to split her focus. High level units (Level 30+ recommended).
Use shield units to draw her focus on one side, then deploy attackers from the opposite side. Shielder health and defense. Heroine.conquest.rar
For tougher bosses like the Boxer, use "vine" units to stun them continuously. Time your placements (about every 1 second) to keep them locked near your high-damage AOE units. Pure stat check
If you are stuck, spend a few rounds just trying to land hits. Focus on increasing unit lifespan first so they survive long enough to deal damage and generate EXP for you. Heroine.conquest.rar