Cancellation of the gift

Ria and Mia are two adult sisters. Ria is the elder sister and Mia the younger one. Both the sisters were orphan but had huge properties bequeathed to them by their now deceased parents. Mia first got married to Ravi whereupon Ria started living in the same residence with Ravi and Mia together. Ria met with an accident and lost both her legs, Ravi and Mia started taking great care of her even using their savings to bear medical expenses of Ria. Ria after 2 years thereon decided to gift all her share of the properties to Mia. After 5 years, Mia then conceived a child and found it difficult to take care of Ria. She requested Ria to go to a hospice, where she could be taken care of. Ria angered by this refused to do so and started living separately with a maid, she demanded that the gift of the properties made by her to Mia should be cancelled. Mia refused to do so. a. Whether the gift of properties by Ria to Mia is valid? Whether Ria can oppose and seek for cancellation of the gift? If yes on what grounds under Contract Act, 1872? b. Can Mia claim from Ria the expenses undertaken by her for Ria’s medical expenses? Explain with legal provisions in Contract Act, 1872?