I always start with Meki Pendant + 2 mana potions, then grab Tear and Chalice, so mana is pretty much a non-issue, and when I said back off, I meant outside of the enemy's immediate attack range once they exit the pool. You kind of have to build her specifically for sustained harassment if that's what you want and pretty much give up your chance of getting kills unless they are seriously overextending, but the option is there and it can be an effective one, especially if you are in mid with the enemy team's only carry and forcing them to constantly turret hug and/or return to base to heal. It is also true that she does wind up mostly there for stuns/roots/shields/mr-shred in team fights with this build, but she also draws fire off her team mates which she can heal right back, so she's kind of an off tank. You'll also probably have a huge exp advantage over everyone else, (I've been 4 levels above everyone else before with 0 kills) so mid game you can be a pretty dominant force.
More specifically, my build order is Tear, Chalice, Boots of Speed, Hextech Revolver, Spirit Visage, WotA (from revolver), Ionian Boots, Archangel's Staff, Rabadon's Deathcap if I've become the carry, or an appropriate aura item if someone else has. W,Q,E, then R>W>E>Q. It's a little different, but gets the job done in a subtle way.