If you wait on the top level she should teleport into range (or run up the ramp between the two levels), especially if your creature attacks her while she is on the lower level. My creature (with a mage head) stayed near the top of the ramp, where it could attack most of the places she can teleport to.
Hopefully you should be able to do damage faster than she can heal when she teleports away. As a ranger I found it best to run/jump in close and use Splitting Arrows, rather than attack from a distance. She teleports away after being attacked, so try to get your strongest attack in first, then follow up with whatever you can until she teleports or you finish her off.
