Need Help With My Own Child...

I am a co-owner of a in-home preschool. The preschool is located in the basement of the other co-owners home. We are new to the preschool / daycare world (as we provide full day care) and I have no choice but to bring my 3-yr-old daughter to work with me. I love having her with me all day, but she is having a hard time sharing her mommy with other kids. She could be perfectly content playing with the other kids, but once I am in her sight she will come crying and whinning to me. This especially happens when I am trying to console another child. How can I help her realize that she has to share mommy while we are at preschool? I am to the point where parents are not wanting to send their kids to us, because of the crying and whinning. I also feel like giving up and going back to not working at all. It is stressing my partner and I out and I don't know what to do.

Any suggestions would be appreciated....thanks.