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Are you able to catch her? it sounds like she has an injury and would benefit from pain medication and rest. If you are unable to see any wounds on her foot, then I am less concerned about a condition called Bumblefoot but she may have another injury and she should be evaluated by a vet if you can or at least caught safely if you can do so and give her a thorough examination to determine if she is unable (i.e. has a fracture or some type of neurologic injury) or unwilling (soft tissue injury that will resolve with time, rest and pain medications) to bear weight.
Does she have any trouble with her wings? What kind of bird is she?