This is normal. My son did it too. Don't run to the rescue when she starts to get upset. Try to stay in sight.
Somewhere I read that you should leave her in a room, tell her you will be right back, leave for a few minutes, and then come back in the room and say, "Here I am." or something like that. This helps them understand that just because you are out of sight, you aren't gone. I said, "I will be right back." every time I left the room and he began to understand.
I would also start leaving her with family members or the person who will be keeping her when you go back to work for brief amounts of time to get her used to you not being there constantly. Make the goodbye very brief, DON'T let her see you upset or sad if she starts to get upset, and ask the caregiver to distract her after you leave. NEVER sneak out because it will make the separation anxiety worse.
It will get easier. Good luck!