S.C.
It sounds like you have done everything possible to try to comfort her and ease transitions and calm her fears. Have you ever tried to do a bit of the opposite? It may be that she's getting herself all worked up because it is routine for her to have drama and have you react in certain ways. Try not to expect her to get upset and try not to explain where your going and how long it will be. With her age you might be able to switch it to - fun to go to daycare. First change what you are saying. When its time to go - be happy and say something like "Its time for an adventure!" Then make saying goodbye for the day short and sweet with a quick hug and "You go have fun playing! Wish I could do that all day. Bye Bye." and leave. Or pretend your secret agents on the way there then say something like "OK here's your mission if you choose to accept it.....create a picture with a secret message in it." Or whatever might be fun to her. Just don't discuss it even if she asks questions. The secret agent one works well because if she starts to ask questions you can look around funny and say something like "Its not safe to talk, someone might be listening." Then do the mission impossible theme. But she might be too young for that so whatever is her thing. Just make it fun and different and ignor anything that seems like she is getting anxious. It helps if you can be goofy. It might take a week or so but I'll bet you see improvement.