I know it's hard, but you need to address your feelings. Talk/vent to someone else when you're sure that she's not within earshot. The pregnancy hormones are making an emotional separation even tougher on you (our little angel is already five months old, and mine are still fluctuating).
Your daughter will take her cues from you. If you talk about how excited you are for her to start school and make new friends, she will be excited too. If you buy her new clothes and tell her how special it is for her to be getting bigger, she will be proud of herself for this next step. If you smile and wave when you drop her off (while squeezing your fists until your palms are bloody to keep from crying), she will be as brave as she can.
Remember this, you have done your homework and are doing the best thing for your daughter. The best way to thicken her skin is through exposure to other children. In my opinion, this is done much better in preschool than in kindergarten - there are fewer students per teacher/aide, the time together is much more limited, and the teachers are better able to continuously monitor how your daughter is doing. If you are overly concerned about any one area, talk to the teacher(s). Ask how to communicate on a daily basis (in 3 yr preschool, the teacher gave all the parents a verbal report every day and a chance to tell us if anything unusual happened; in 4 yr preschool, we use a journal with written notes - typed with the acitivities they enjoyed and handwritten notes for anything out of the ordinary) and to ensure consistency between home and school. Tell the teacher(s) about your anxiety - they're used to this and can help you through the transition.
Finally, remember that picking her up each day is as important as dropping her off. Ask her to tell you about her day and really listen (this will be hard with the new baby, but it's critical that you make time for this). If she knows that you care, she will NEVER feel like you are "sending her away." Chin up, mama... this, too, shall pass :)