My oldest son had a lot of separation anxiety when he started school. He's very sensitive, too. It is so hard to see them upset and anxious, but for my son, I think it was very helpful for him to learn that there are kind, caring adults at school who really are looking out for him when I'm not there. He loves school now.
Two things that really worked for us were kissing hands and worry stones. We read the book "The Kissing Hand" - great book, really reaffirms that a) it is OK to be sad and nervous about leaving mommy and b) mommy's love and thoughts are with you, even when she's not. It has been two years, and he still wants his kissing hand every morning.
For the worry stone, I took a stone necklace pendant I had, and pinned it in his pocket (for your daughter, she could wear it as a necklace). I told him whenever he felt sad during the day, he could rub the stone, and when he did, I'd send a hug his way. After school I'd ask, "Did you rub your stone today?" and when he said yes, I'd say, "I thought so. I was sending those hugs. Did you feel them?" A little deceptive, maybe, but the truth is I was
thinking about him and sending hugs in my thoughts!
Anyway, he used the stone for about a month before he didn't need it anymore. I think at first, having something physical to touch was important, then later when he was doing better, the kissing hand was enough.
Good luck! I hope her transition goes well. As hard as it is, I think it is true that the more calm, confident and upbeat you are about the separation, the easier it will be for her to let go of the anxiety.