I'll second Sarah & add you might tell her that if she's bringing more than your maximum it's important that she cancel her booking and find one that fits her needs asap- before other listings fill up. You are just being a good host and looking out for her interests. To look out for your own interests you are doing all of this messaging thru the airbnb site, right?
In the context of how we manage our listings "Not suitable" is a friendlier way of saying "Hell no" My listing is not suitable for events or pets and there will be neither puppies or parties cuz I say so. Sally