Long story short*, DD's preschool teachers sent me a very nicely, politely, and carefully worded "Back off mom and let us handle it," email regarding drop off. Objectively, they may be right - I think there are times moms lag behind in realizing what their kids are capable of. (And sometimes, they're leading, too.) Subjectively, well, I still know my kid better than they do, and my hackles were raised (though that wasn't their intent). I'm willing to try their way with drop off, but I will also be the one to deal with the bulk of the consequences if it goes badly. Of course, maybe I'm being too protective and it will go great. Who know?! No one until we try.
But I'm feeling that annoying mix of shame ("oh no, am I the one holding my kid back?!") and protectiveness ("but they don't know my kid like I do") and frustration ("hey, maybe they could have said something earlier, if this is how they felt") and anxiousness ("what are the consequences of trying this going to be?!").
Odd are, I am the problem. (As my husband put it

he is certainly straightforward, though he was trying to be kind at the same time. But it's true, kids behave differently around parents than other people.) And this might help. But darned if I am not nervous about it. And we have to wait two days to try since preschool isn't until Monday!
*Ask for the long story if you want it. I'm being lazy about writing it out.
Re: Getting All Defensive (Venting)
BFP #1: 05/2012 DS born 12/30/12
BFP #2: 02/2014 Natural M/C 03/2014 @ 7 weeks
BFP #3: 06/2014 EDD: 02/17/2015 M/C @ 7w2d, D&E 7/15/14
Is there one teacher in particular who she gravitates to? Maybe that teacher could be more actively involved in the process, so LO is never along during the transition from drop off to her first task.
There are only 2+ months of school left, right? I still stick by what I said, try baby steps. But really, she's only there for a little while longer. Maybe next year you can establish a new routine.