Firing a difficult client

[mom-in-alberta]

Haha... I saw the kitty right away??

Anyway; I agree that you need to come up with a discipline plan right now and stick to it. You're right, it's not fair that she dictates whether others are "allowed" to interact with her. We ALL have off days, but it's not a license to scream or be aggressive or what have you.
So be it time outs or another method, it's just going to have to be consistent follow through. And yes, mom/dad MUST be on the same page. Tell them exactly what the challenges are and explain why it's not acceptable.
"She tends to melt down when I am not able to attend to her want/need immediately. But patience is a very important quality in group care. Together, we can help her learn that it's OKAY to wait a minute or two." or whatever message you want to get across.
Sometimes we need to teach the parents, as much as the children!