Oh, dear. I can just imagine how mad you are at your cousin.
All you can do now is keep Coco quiet and hope for the best. I belong to several forums and it does seem like most of the time an ACL tear does require surgery. We had one lady whose Maltese tore his climbing over a gate while they were visiting and he had to have the surgery. A year later he tore the ACL in his other leg and needed surgery again!
One thing you can expect with these little dogs is to expect the unexpected vet bill and try to be prepared.
Unfortunately, no pet insurance will cover pre-existing conditions so if Coco needs surgery, you'll have to pay for it yourself. You can ask if your vet will let you pay on a payment plan. Many vets will, but it's been my experience that most specialists expect to be paid in full for surgery.
One option is Care Credit. They offer financing for veterinary services.
http://www.carecredit.com/
Do you have any sort of account set up for emergency vet bills? Most people I know opt to put money in a special account every month instead of paying a pet insurance premium every month since you never know what they will and will not cover. If you don't have an account and Coco doesn't need surgery, now is a great time to set one up.
Another idea borrowed from someone on another forum is keeping a credit card just for vet emergencies and then paying it down as quickly as possible so you don't end up paying three times as much for the procedure.
Hopefully Coco won't need surgery.
