Hello, I'm Dr. Deb. Thanks for requesting me; I'll do my best to help you today.
I'm sorry that Bella has been injured.
I don't have personal experience with use of Zanaflex in dogs so I researched it on a veterinary database. Fortunately, I couldn't find much information about this drug nor a safe dosage range.
Therefore, I think it safest to avoid it's use since I wouldn't want to cause Bella any harm.
Another option for you to consider would be Aspirin at a dose of 10 mg per pound of body weight twice a day, with food to avoid stomach
Another option would be Acetaminophen (Tylenol) at a dose of 5 mg per pound of body weight twice a day.
Both of these drugs have anti-inflammatory as well as anti-pain properties which may be effective in this situation.
My only hesitation about the use of either Aspirin or Tylenol would be that it might interfere with what your vet would want to prescribe if she has to be seen. However, several doses should be fine and, hopefully, will provide much needed relief for her.
I hope this helps and that she's feeling better soon. Deb