I did it at level 8 with umbra gear plus a bunch of healing potions and repair hammers. Made it through on first go with only one near death experience. I did lose all but one of the NPC's though. I wouldn't want to attempt this any level above 10
There's a much easier way. I just defeated her yesterday at level 4. Take the headshot as detailed then run all the way out of the area. She will follow you outside. Hop on your horse and ride back to the West gate of the city. She will still be following. Head inside the city and watch her take on all the city guard. Eventually she will fall allowing you to loot not just her but a dozen or more city guard. You can then slow walk (encumbered) to market district where you can sell all the city guard armor/weapons and buy lots of repair hammers to repair umbra gear getting you lots of merchant and repair points in the process. Remembered this trick from my first playthrough of the original game.
