Please don't tape the leg, you'll most likely do more harm than good, however well intended and may cause permanent disability.
As said, your Mum MUST take the bird to a vet as soon as possible! Poor baby will be in agony if it's leg is broken! Please get her to read this.
In the UK, in the US too I would imagine, withholding veterinary treatment for a pet in need is against the law so please get her to do the right thing for the baby
