That a really common thing with kids her age. Just keep doing your normal daily routine and try to talk to her while you are out of sight. She will get over it.
At her age, she is just learning to understand that things (you) don't actual disappear when she cannot see them and she will soon begin to understand that even when she cannot see you, that you are still there. Just give it time and before too long she will be fine when you walk out of the room. It is a stage that doesn't last too long and although it can be frustrating, she is developmentally on par.
She'll get it I promise. In the mean time just talk with her and let her know you are leaving before hand and keep reassuring her while you are gone (when possible) that you are still present (in the house)...she'll be fine. Don't hurry or try to make it better right away......she WILL adjust. I promise.
