Hi mml
Have you thought about taking her maybe to a childminder for a day each week? My youngest is a very sensitive little boy - he'll mix with most children (apart from one who was consistently horrid to him from a very early age) but if he gets upset, its quite difficult for him to get over it. I find that a childminder is much better suited for him than a nursery purely because of the smaller number of other children.
In all honesty, it was difficult at first because I only worked part time then & it took a good few weeks of him crying, clinging to my legs & begging me not to leave him before he completely settled in I clearly remember one morning, I took him and had to physically strap him into a buggy so I could get out of the house. I got as far as the garden path, turned & looked through the window & he was happily playing with the other children!!!
On my days off, we used to go to the wacky warehouse and also a SureStart group which was absolutely great (so much so that now I'm back at work full time, I miss it maybe more than he does!!).
My childminder also collects older children from the local school so he's used to going there which will be a great help (hopefully) come September when he starts.
A small part of me thinks that maybe because you have such vivid memories of your own shyness, you're worrying more than your daughter. At the end of the day, you sound like you're doing a great job!!
Lots of luck to you all