Vet said my injured canary will never be able to use her leg again...?

You are right to keep her and her mate seperate for awhile till she is feeling stronger and get used to only having the use of one leg . If the vet say the leg is stiil getting a blood flow then it is not worth risking trying to remove the leg as there is a very high risk of her dying if the vet tried to remove it. Canaries aren't the most agressive birds but will of course bicker and argue do happen especailly at this time of the year when everyone is pairing up and trying to get best nest and protect it. Your poor bird has just been unlucky she damged her legs. I would make sure you have plenty of nest in the aviary i always make sure mine have more than pairs of birds. And make sure have plenty of nesting material. Mine seem to like hay. When she is stronger you can try reintroducing her and her mate. there maybe alittle bickering to start but hopefully not to much,. It is so important that you don't overcrowd your aviary as if there is to many birds they are more likely to argue. If she still is being bullied it might be worth just keeping her and her mate seperate till breeding season is over. It is great to read someone on her has taken there pet especailly a bird to the vets.