1. Your mother is the rightful owner of 50% of the flat. Period,
2. Neither she nor you alone can put anyone's name as a nominee of the flat,
3. She can gift or will her share of the flat to anyone which you can not stop,
4. You can file a declaratory suit praying for a declaration that you are the actual owner the flat since you have paid the entire consideration while buying the said flat,
5. If the Court so declares, you can be the absolute owner of the entire flat,
6. If your mother dies intestate, you shall authomatically inherit hwer share of the said flat.