1. The ownership to a property vests in the person in whose favour it has been registered regardless of whether he paid the sale consideration or not.
2. To impeach her ownership and seek a judicial declaration of your own you are required to file a lawsuit in the court to seek court's declaration that you are the owner of the property. The documentary proof of remittance of funds by you can be used in the court.
3. Your mother can, however, take the defence that you intended to register the property in her favour.
4. Do seek a stay order against the sale of property by your mother.