We left our 2 1/2 year old and it was definately tougher on me than her.
We made a little calendar with some pictures of us and stickers stating how many more days until Mommy and Daddy come home. They crossed off each day and would tell her...only 3 more days, etc. She seemed OK knowing when we would return. We also called and spoke to her daily.
Another thing we did was leave a gift bag for each day we were gone, she LOVED that. This time I bought her a new 'baby' of her own and will give her something each day we are gone for her new baby. Plus some books on becoming a big sisiter.
Try not to worry...she'll be better than you most likely...but that is a good thing.
Good Luck!