Polly may do quite well despite her disability. Since she has lasted this long hunting for herself she may have figured out what she can and can't do. The first year is the toughest bar none, and she is only a few months to making it past year one!
For hunting, she needs to be able to fly more than use her feet. So long as she can kill and subsequently get to her prey, she could do well. She may never be able to catch and carry heavy items, but she there are lots of smaller birds she can catch and carry. There are lots of larger birds she can catch, kill, eat on sight, or dismember into small pieces if she needs to transport/cache. More work, but it sounds like she's adapting well. Or she might have the strength, just not the dexterity in that foot, in which case she will simply compensate with the other one.
Of more interest is her ability to breed. She needs to be able to support herself and her mate during copulation, tends to be a quick act but they are rather, umm, "busy" in the spring so it may be a question of endurance for her.
As for leaving, she may decide not to ... she knows where she is and can hunt her safely/effectively and that may be enough to keep her there. Other birds stay to defend territories year-round, other young birds (think New York City) and there is no identifiable reason why they decide to hang around. And there will be plenty of food for her year-round in Montreal if she stays.
