pre-school and shy 3 yr old

I have a very shy 3 yrs old daughter, and she's going to start pre-school in two wks.
She's very shy with people she doesn't know, and gets really uncomfortable when they (unknow people) talk/look at her.  It takes her approx. 2 hrs for her to feel comfortable and start warming up.  
I'm a stay at home mom (she's my only child), and she doesn't interact with other children her age, with the exception of a frinds 5 yr old with whom she plays.  That's why I decided to start pre-school.
My problem is that in all places I've visited, they won't allow me to stay with her for a couple of hrs until she gets used to people, because they argue that she'll get used to it (me staying with her for a couple of hrs during the first weeks).  I wonder if this could be harmful for her since she's so shy.  They suggested leaving her for shorter periods of time at first.  She gets real bored at home and needs to burn energy.  Do you think this is the right way for her to start socializing and playing with other kids?  Won't it be too traumatic for her?
Please give me some guidance
Thanks!!!

[Kevin Kennedy, Ph.D.]

Yes, you are doing the correct thing. The programs are also doing the correct thing by not permitting you to stay with her. That would only reinforce the reticence. You'll have to bite the bullet, so to speak, but it will be fine. She simply needs practice, so to speak, being around other people. If the program allows, phase her into it by gradually lengthening the amount of time she's at the program. Do this in collaboaration with the staff.