Yeah, you have to watch out for Major in this one, just like DM17. I think the action happens mostly on one edge of the map where there is a semi-circular tall shaft and a vertical launch pad. Bots will jump on that repeatedly and will get fragged mid-air by whoever is in the area. I think that's how Major gets many frags really quickly. Your best bet is to be around that area, on the top of that shaft. It's still not going to be easy but you could steal some frags from her this way.
There is also a ledge nearby with 2 stairs leading up it from each side. That area is pretty traveled by bots as well. You could score some frags there if you can handle the railgun. And it is pretty close, so you don't have to travel far to cover both of these locations.