Do you have lillies in your garden?
They are highly toxic to cats, but saying that, they are soooo toxic she would have gone down hill last night, not this morning. But there could be other plants that have upset her system.
If this is the case, hopefully the vet will be able to 'wash' anything out. Good call on taking her to the vet. Sometimes wait and see is not a risk worth taking.

But as a note to everyone, Lillies are highly toxic to cats and the smallest amount will cause the cat to go into renal failure within hours. They don't have to eat the plant, if they just brush past it and get pollen on them, they can later injest the pollen by cleaning themselves.