My response is simply to make YOU feel better that transitions can be tough for the child.
I've always been a full-time working mom (even during 5 months of chemo after the birth of my 2nd child), and made the decision to switch from having the mother of a friend watch our children in our home to going to full-time day care 2 years ago. It was hard, but it was the BEST decision we made.
Even when I was laid off last year, we still kept the kids part time (in part to keep them acquainted with the process knowing I was going back to work and in part to give me the time to find a new job/interview, etc). Part time is harder than full-time, for sure.
Our son transitioned into a new class 6 months ago (at 3.5 years) and had a really tough time. He knew almost all the kids, but he had gotten really comfortable in his previous class. His little sister had no problem.
So, I think it really depends on the child. But, if you put your confidence that the providers know how to do it and how to help your child transition as well as possible, it will help reduce your anxiety. She'll pick-up on your hesitation, anxiety, fear and feed off of it.
I have no regrets having put my children into a day care facility because I believe the education, socialization, etc. they've received is far greater than it would have been if we'd continued to have the other person watch them (though she loved him unconditionally).
Good luck - don't be afraid to tell the director/teachers your concerns and ask their advice. Chances are, they've encountered this many times before.