Hello, I'm Dr. Deb and will do my best to help you today.
I'm sorry for this concern about Miss B but accidents of this sort do happen from time to time, unfortunately.
Depending on how well controlled her diabetes might be, hypoglycemia is a real possibility over the next 12 hours or so since she received double her normal dose of insulin.
You'll want to keep that blood sugar from plummeting too low by feeding her small amounts of food every several hours. You could also offer her a small amount of honey or pancake syrup every hour or so as well, especially if she becomes lethargic or has balance issues.
More than likely, she'll be fine if you provide enough food/honey to keep her blood sugar high. However, if she shows signs consistent with hypoglycemia (trembling, seizures as the worst case scenario) and you can't eliminate those signs by giving her honey, then an ER visit may be prudent.
Just to be on the safe side, I might skip her next dose or only give her 1/2 of her normal dose.
I hope this helps. Deb