بسم الله الرحمن الرحيم
Whatsoever Ms Zamrath spent for the treatment of your sister if she did it with the intention of debt then after her death the debt of Ms Zamrath will be paid from her leftover property. However, if Ms Zamrath spent it voluntarily then she has no right to take back her money after her death which she had spent. However, if the heirs of Zaibu Nisha give her something with their mutual consent then there is no harm in it. The property which father bought if Zaibu Nisha invested in buying the property as a partner then Zaibu Nisha shall be deemed owner of the part of land equal to her money thus after her death her share in the property shall be divided among her legal heirs as per the Shariah division after paying her debts etc if any and due expenses of her funeral rites.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.