What kind of build are you playing? Melee or magic? I'm melee and hardly take a hit against this boss as she doesn't attack that much.
If you're melee and go down the right hand side to the last column and two hand your weapon then you can run up and whack off a good bit of her health bar. When she teleports there will only be a couple of clones so go back up the columns and look at the worshippers. They'll be raising their hands and and facing the real one. Once you know what one it is you can run over and finish her off before she teleports for the second time. If she does manage to get away then do it again or go hell for leather and hopefully you'll get the right one before it gets too overwhelming.
I'd also say if you have found Patches already in the Tunnel City then you can go to Islands Edge and kill a few of the skeletons at the start for souls then go back to the Nexus and buy grass from him before going back and trying it again. Archstone of the Shadowmen is actually pretty easy if you avoid the big demon and red eye skeletons. Also, take a bow for the flying things and you'll be able to get a big chunk of it done when you're fairly under levelled. That should let you level up a bit and hopefully go back and finish off the Idol.
If you've already killed the Flamelurker and Tower Knight then a run through the Inner Ward is excellent for collecting grasses.
