Thank you for the additional information. It is helpful.
Dogs who will not put weight on a leg could have a dislocated hip, or a knee injury such as an ACL tear. You can read about dislocated hips here:
And read about ACL injuries here:
Since she is not putting weight on it, it probably is NOT a pulled muscle. I would have her seen by your vet as soon as possible.. If possible, contain her in a crate until you can get her seen. If it is a dislocated joint it is best addressed as quickly as possible. In addtion, buffered aspirin can be given to a dog with a dosage of up to 5 mg per pound every 12 hours. Keep in mind that a dog's body does not metabolize aspirin in the same way as a human and thus should not be given more than a day or two without contacting your Vet. The aspirin may need to clear your dog’s system before other medications can be given, so keep that in mind if you decide to give aspirin and be sure and tell your vet when your dog is seen. Read side effects and precautions here.
If aspirin is used, your vet may not be able to prescribe other drugs until it clears from your dog's system. I'd probably hold off on the aspirin if you are going to get your dog in pretty quickly.
If Gizmo was my girl, I'd crate her and only let her out to eliminate and have her on a leash then. Keeping her as inactive as possible will help prevent further damage until you can have her seen. It is hard to say which is the problem since all the possibilities could occur given the situation.
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