How long have you had the daycare going? It could definately be a sharing thing. She's not only sharing old toys, and you, but also her santuary.

My little girl is very social outside of the house with just about anyone, but she has trouble when people she doesn't know (or doesn't know well) come into our home.

This is quite a huge change for her on all levels. At her age she's not quite at the stage where she is able to label her feelings as jealous, or overwhelmed.

Maybe you could go over the day with her each morning before the children come. sit down and tell her who is coming and what you will be doing. She probably won't remember it all the just the act itself shows her there is order in the caios that is a daycare and she maybe feel more prepare and better able to cope.

Also talk excitedly about what she will be able to do with her new friends today. ask her what she likes about everyone (leave the negatives out). Give her special things to 'show her friends' or have her help make cookies or something that she can share with them.

Keep all this going consistently for a month or two. One week won't cut it even if you do see improvement.