So I apologize up front as I’m not sure entirely what causes this boss to spawn as I was randomly exploring and ran into her.
However, you will want to go to the crash site in the very north of the map- it’s the hub area with a bunch of NPCs. Make your way left to a longer corridor and you will run into her. There is a save point a few screens away.
Dolly is very quick and she likes to play cat and mouse. Don’t follow her. Let her come to you and unload in her face as she charges and then jump over her when she throws her spiked ball. When she gets low on health she will do some jumping slams. Jump dash over those and rinse and repeat. Not too tough overall. I used a combination of the cloudburst rifle and coburn launcher.
Enjoy your achievement and enjoy playing this fantastic little game!