We also did the slow transition when DD started.  She first went at 3 mos (it was the only way to get her a slot at the place we loved), and I started work when she was 6 months.  So in the beginning I'd drop her for an hour while I showered or got coffee or whatever.  Then it was a couple of hours while I worked out or ran errands.  By the time I went to work it was no big deal for either of us.  And this didn't take 3 months to transition, a week or 2 should be plenty.  

The thing to remember is that kids go through transitions.  So sometimes for no apparent reason, she'll have a really hard time with drop off.  Usually during developmental milestones, or when she's tired, or when she's teething, or coming down with something.  So if Rory becomes clingy all of a sudden, it doesn't necessarily mean the preschool isn't working, it may just be a phase.  Use your mommy-intuition.  

We also have a great book called Owl Babies about baby owls that wake up and their mommy isn't there -- but she comes back, because Owl mommies always come back.  DD actually uses that phrase when she's nervous.  

--R