1. She's a lightning rod. In other words she had great resistance and health so she can be placed in order to soak damage from magic users.
2. Great for those moments when you need a good fighter to kill off certain packs but do not want to drop down a new unit and then withdraw them every time.

Angels in general have quite the good use when you want to kill off certain mobs or defend against magic users. They're like on-demand valkyries/bandits that will demolish whatever you let them fight. Basically you place them down at a key location and let normal mobs pass, then when the specific enemy appears you activate the skill and kill it.