A. She may have hurt (soft tissue -ligament/muscles/joints- or bone injury) herself on that leg. I would recommend to take her to your veterinarian for a check up and appropriate treatment.
She may need pain relief medications and potentially antibiotics if the nature of the problem is an infection (for example an abscess due to a cat bite).
The differentials unfortunately are many and I cannot be more specific at this stage. If you require to discuss this problem any further please request a consultation.
Your account has been reactivated.