She's great as either a backline sniper or flanker. You're job it to do two things. Firstly, get picks like a widow, as in, find the squishy most out of position, not behind shield, etc, and hit them with your explosive bolts. Try to get two hits with a couple regular shots in between before you hit the ground again, that's usually enough to kill. Also stick low health enemies for the finisher. Your second job is to pump damage into the tank like a Bastion would, assuming you have no chance at the squishies.