I would say she's doing it because financially she'll be better off with two children from one family. I don't think she's obligated to give you the place first, that certainly would be the professional thing to do.
As someone said, if she's so hard to get onto, then you might be better off finding someone else anyway. What if there was an emergency that you needed to contact her about? Though she's probably got caller ID and didn't want to talk to you until she saw the other family.