Hi Danielle,
Your daughter is undoubtably going to be sad when you leave. If your school has a "meet the teacher" day, it helps for her to meet the teacher(s) and see her class before she is going to stay there. What also helped for my daughter is understanding what her day would be "you are going to have circle time, then go outside and play, then a snack, and mommy will pick you up after your craft". The routine will likely be the same each day, so ask the teacher what their schedule is. Make sure your daughter undertands after what activity you will be there- it makes more sense than telling a time, or saying something like "soon" or "a little while". It also reminds her of all the fun things she is going to do during the day. Most kids cry when you leave. Most kids stop crying right away. She might also cry when you pick her up. Make sure you keep communicating with her teacher- they have been through this MANY times, and have lots of advice. Her teacher can also tell you how she is doing during the day when you don't see her. Good luck!