Will to my daughter n her care takers only

Sir, our house help is the second wife of a person who gave his brother's name in the court instead of his when getting married to her in Mumbai. He was already married with children but did not reveal it to our helper until after court marriage which she had insisted for. Her name is not there in his ration card. They have a 12 yr old mentally challenged daughter now. Our helper saved her hard earned money for long and has bought a room in a chawl in Mumbai and has registered it in her name. Her husbands name is mentioned in the papers as wife of so and so. Now her husband and his first wife and children are behind the house she has bought for herself and her daughter. She has a ration card without her husbands name in it. Her mother takes care of the daughter when she goes for work. Now she wants to make a will stating that after her the property will go to her daughter only and her mother or anyone else who will take care of her daughter can use the rent out of her house for the expenses. She doesn't want her husband or his first family to take care of her daughter. And post her daughter she wants the property to be given to a orphanage only. She doesn't want anyone else to claim their right on her house. Can you please let us know if that is possible and how should she go about making a Will to that effect.