WEll, here the school term started 2 weeks ago, and my dd1 went for the first time. I was a wreck beforehand- I understand totally what you mean. Up until now, I have been the only real influence and source of knowledge in her life, but now I am relinquishing some of that control to teachers I don't really know. It's like she's not wholly just mine any more! I do realise, however, that that is a really selfish way to think. dd was desperate to get to school, and is really enjoying it, which does make me feel better for her, but sad for me! At the moment she is only in until noon, but she can't wait until she can be in for a full day! The good thing for me is that, at the moment, no sooner have I dropped her off and walked the dogs and tidied up, it's time to pick her up again.
I would honestly say it's one of those things that isn't as bad as you think! When she comes home from school, we have things to chat about and "homework" to do together, so I actually feel like we are getting quality time together, and it means I have a chance to spend time with all 3 kids individually, rather than en masse (trying to see positives here!!)
It is nervewracking, though. And when they come home and tell you noone wants to play with them, it breaks your heart! But the next day they seem to be on top of the world, so I truly think it affects me, more than it affects her.
Good luck!