While we can give slightly higher doses than what was prescribed, she has had quite a high overdose.
Cats can safely tolerate 0.5mg/kg, or 5 times the therapeutic dose, but she has had double this.
There is some concern here, for possible gastrointestinal signs, or even a stomach ulcer or kidney disease.
As it was a one off, hopefully she will not suffer any ill effects, but it is possible.
As it has been more than 4 hours, it is no longer useful to induce vomiting.
However, we could start a fluid drip and offer activated charcoal.
If it is an option to have her seen out of hours to do this now, this is the option with least risk.
The alternative is to monitor closely for the next few days to ensure she remains well and has no symptoms.
We should offer a bland diet of chicken and rice and plenty of water.
I would not give any more of the medicine, even when next due.
It is also important to call your vet once open, to make them aware.