The pole on the right side of the path is used to turn off the traps. Since you already sprung those, the pole won't work now
Dunno why you're having trouble getting into the cave. You can't really kill Izbelah at this time. She teleports away and leaves some stuff behind. After that you should be able to get in.
You may want to try this again by going back to an earlier save (you should have an auto-save from just before heading to DE). I've never had a problem here, but a couple of times, weird things happened to me in the Ice Temple that were cleared up by quitting to desktop and reloading.
Nightowl2