Yep, I think most bfers go through this at some time. Hopefully you can find a solution or make peace with it.
Will she take a sippy cup at all? DS refused bottles but then we bought him a bright purple sippy cup - he LOVES it.
I think if boobies are your only "settling weapon" then there may be too much pressure on you soley. Have you talked to Shel about trying other things? When you get into the habit of always "boobing" to settle, it can get to the point where it seems like nothing else will work and you don't want to risk it by trying anythign different. But while Jaz may demand boobies from you, she may be quite happy to have something else - singing/rocking/whatever - from someone else.
At her age also I guess she may not really need milk feeds quite so often, so you really should be able to take some time out. Why not arrange some time out with friends and leave her with Shel to get on with it. they'll find some other way to settle. (don't mean to sound blase about it, I really have been here and this is what we did with my DH & babysitter...and it worked).

DS still does constant night feeds some nights and it drives my balmy at times.