J.F.
I did 2 half-days the first year, and then 3 half-days the following two years. I knew that we were going to do half-day kindergarten only, so I thought that was enough. Transition to K went just fine.
If you're going to have her do full-day K, you might want to consider doing something like 3 full-days for pre-K. My son did have an adjustment period going from half-day K to full days in 1st grade. He was very tired by the end of the day and would sometimes cry once we got back to the car at pick-up time.
This transition lasted about 2 months. It didn't affect his school/academic progress at all, however. He just needed time to adjust to the new schedule.
Hope that helps.