Is it permissible for the seller to demand a higher price five years after the sale and her refusal to register the contract, and would the additional money be permissible (halal)?

If the sale has fulfilled its conditions and pillars, then it is not permissible to revoke it or to demand more money than what was agreed upon in the contract, even if it is not registered in the land registry, due to the Almighty's saying: (O you who have believed, fulfill [all] contracts). This action is forbidden for the woman, and she must fear Allah and not demand more than her right.