There's actually a pretty simple way to kill this boss even if you are doing a 'Not Even Once' run. I would recommend getting the Abyss ultimate ability before the fight. She has pretty long range and a few really powerful AoE attacks, but if you are sprinting you can actually avoid basically everything she dishes out at you without problems.
Wait until your ultimate is charged then use it against her which should suspend her in the air for a few seconds, doing really good amounts of damage and giving you a few seconds to get in close and hit/shoot her a few times as well. Depending on what level your ult is at (
) you should be able to rinse and repeat this process five or six times and have finished the fight.