In this video guide I will show you how to defeat Astarte the Fallen Angel. Another interesting fun fight. So there are a couple of ways to do this.
First way is to fight her on horseback with Strife, and just simply keep shooting her. Or if you wanted to go for the side objectives and kill the minions you could fight her on foot. If you choose to fight her on foot I would recommend laying down the caltrops in her path and shoot her as she goes by. Probably not the fastest way, but still entertaining.A few things to look out for.
After she is done going around in a circle, she will start doing some rampaging dashes. These are random while she tries to hit you and flies all over the map. The other thing is, when she is closer to death she will start having lightning strikes on the map in random spots. Just pay attention to where they are and avoid them.
This fight will only take awhile because you are on your horse shooting, versus using all of your arsenal. But nonetheless keep shooting and she will fall before you know it. Once the cut scene is over the achievement will pop.