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).
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.
Place shield units on both sides to absorb projectiles. Place attackers in the center with high range. Attacker range and damage.
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.
Focus on shielder block/health and thrower range. Keep a shielder next to her to distract while throwers chip away. Thrower range and damage.
For more niche tips or technical help, check the Heroine Conquest Steam Discussions or the Itch.io comment section. Are you having trouble with a specific heroine , or Heroine Conquest by BadColor
Use shield units to draw her focus on one side, then deploy attackers from the opposite side. Shielder health and defense.
Select your troops using the 1, 2, and 3 keys. Right-click on the battlefield to place them.