It is very hard. Benjamin's first day of kindy, he didn't even want me to take him inside, he wanted to be such a big boy, and have me drop him at the door. Well my heart broke, but I did it. The next four days after that, we had huge crying spurts. We started school on the Tuesday, I remember on the Thursday was the worst day, we actually had the hanging on the door frame thing...where he literally hung on and would not let go.
I knew he enjoyed school, it was just leaving mama that was hard. I would imagine she just feels sad leaving you, I know for Benjamin that was the case. He just wanted to be home with ME, it was such a big change. I reassured him that we weren't doing anything fun while he was gone (LOL), and that it was nice to meet new friends, etc. It did get better, but I'm sure it varies from kid to kid.
I'm sorry, I know it's just as hard on you as it is on her. My heart was sick sending him to school like that, the mama in me just wanted to grab him and take him on back home with me. ((hugs)) and hang in there, it will get better.