It has been my experience that most kids adjust to going to kindergarten very well even without the experience of pre-school. Most of us parents never went to pre-school as kids. However, I have sent 2 of my kids to some sort of pre-school prior ro kindergarten (my third is only 11 months old).
My 15 year old daughter went to daycare for about 6 months when she was 2 1/2 (she started in Feb after a long winter of 2 feet of snow, we hardly got out and developed a bit of cabin fever and I wanted her to have some social interaction because there were few kids in my area). It was a horrible experience for her, she cried everyday for about 5-15 minutes before she would engage with the other kids. This went on for about a month or so. She eventually stopped and enjoyed herself. We moved just after she turned 3 and she never went back to pre-school. She started kindergarten on time and was excited, couldn't wait to ride the bus, enjoyed being with the other kids from day one and never had a problem.
My 5 year old son will start kindergarten in the fall. He started pre-school in October and jumped right in and loved it from the get go.
Both of my kids are somewhat shy and still managed to make friends on the first day of school. My son was at a fellow classmates birthday party 3 weeks after school started. He can not wait to go to kindergarten with the big kids.
If you do choose to hold your daughter back, check into the local high school. My son's pre-school program is part of the high school curriculum (Child Developement Class for the students) it is supervised by a teacher but the kids are taught by the high school students and it is free. He goes 3 days a week. From what I understand most high school's run a similar program, the kids go for about 2 - 2 1/2 hours a few days a week. The classes are small (average about 12 kids) and I think it may be less intimidating for the kids because they become friendly with the teenagers as well and not a teacher who seems more like an authority figure. My son has learned to write his name, most of his letters, he learns about many different things as well...recycling, plants, planets, animals, holidays, etc, they even have a graduation set for the first week in June.
Make the choice that you think is best for your daughter... I guess you could always look into starting her in kindergarten and if things don't seem to be working out pull her out and move her into a pre-school program. Our high school program doesn't even start taking registrations for pre-school until August but the kindergarten registration is just about over... they are doing orientation in mid-May for both the parents and the kids. The kids get to meet the teacher and classmates and even get to ride the bus around the school. The parents meet in a separate classroom and get the run down on how things will work.
Best of luck with your decision,