Yep, the lever is the switch I'm talking about - if you can damage her, you can beat her. I could hit her before I found the switch (using fireball at maximum range), but was unable to damage her.
I thought that once the lever was pulled, she stopped teleporting, but I was wrong (sorry) - apparently my character was simply able to do enough damage to kill her before she teleported.
Apparently, if she teleports before she's dead, you need to use the teleporters (that you activated with the lever) to chase her to the other platform, rather than running to follow her - it's the only way to get to her fast enough.
