I remember crying when my first daughter went to kindergarden. Somehow, it wasn't the same for preschool, but that was with a very dear community friend who felt like a sister to me and my daughter had been at her home many times before.
You say your daughter is well behaved, friendly, and sweet...I'm sure she is absolutely adorable. I promise, so will the other kids be. I promise the teacher will also be and will work so hard to make sure that all the ways children are learning will not hurt anyone else beyond the simple bumps and slight emotional bruises we all get once in awhile as we grow. If you have any concerns AFTER your daughter has been there awhile, or you have any reason to believe there is a problem, by all means, find a preschool where you feel absolutely certain of the teacher, the methods, and the other children.
Hang out for awhile..most preschool teachers will welcome parents for a little while, and SHOULD also welcome unobtrusive visiting at any time, especially if you offer to help out in the classroom in some way at those times. Maybe you could help do reading time, or just sit in circle time at the opposite end of the circle as the teacher, to model for the children and help them participate. Helping at snack time or art time or any time is usually so much appreciated as long as you don't try to take over the methods the teacher uses.
Your little baby girl is growing up a little bit, and this is a big step for both of you, no doubt at all. It is bittersweet--just as that first step, first smile, first word, first hug--all the great and wonderful firsts that mean your little one is doing just as she should and you are a good and loving parent but also mean that she is gradually moving away from that smallness that you hold so precious. But she needs friends--and a friendly little girl will make lots of them. And she needs to learn how to handle herself even when others aren't perfectly attuned to her every need as you have been so admirably during the years when that WAS what she needed. You have given her roots, now you must give her wings. Just little baby ones--she's not leaving the nest yet.
When I read Khahlil Gibrahn, his poem about children is the most profound for me:
"Your children are not your children. They are the sons and the daughters of Life's yearning for itself. They come through you, but they are not of you and though they are with you, they belong not to you.
You may give them your love but not your thoughts,
For they have their own thoughts.
You may house their bodies but not their souls,
For their souls dwell in the house of tomorrow,
which you cannot visit, not even in your dreams.
You may strive to be like them,
but seek not to make them like you.
For life goes not backward nor tarries with yesterday.
You are the bows from which your children
as living arrows are sent forth.
The archer sees the mark upon the path of the infinite,
and He bends you with His might
that His arrows may go swift and far.
Let your bending in the archer's hand be for gladness;
For even as He loves the arrow that flies,
so He loves also the bow that is stable."
Many hugs, much empathy, and a few tears of recognition as I look at my "baby" brushing her hair and beginning to act premenstrual and getting all excited about starting middle school next year. And yes, I still have the photo of her all thrilled in her special pink and purple outfit with matching backpack filled with a snack that she took to her first day of preschool. And once in awhile, I still long for that little girl who only looked to me as her "special best friend", even as I thrill with excitement as I see what she is becoming all on her own.