Dear Sir,

Your mother cannot sell what's not hers.

She first has to lodge the 50% bequeathed by her partner under her name at the land registry prior to selling on the property.

No Spanish Notary will allow the sale of a property whose not under the name of the vendor, it's a criminal offence ruled by art 251 of Spain's Criminal Code.

Your mother would have to hire a Spanish lawyer and do as follows:

1.- Depending on the nationality of her partner, a grant of probate.
2.- Deed of Declaration of Heirs by which she's appointed as the sole beneficiary of the remainding 50%.
3.- Lodge this deed at the land registry and pay any associated taxes such as Death duties. As 5 years haver already gobe by she will not have to pay Spanish Inheritance Tax albeit her lawyer will still have to fill in the tax model otherwise the property will not be registered under her name.
4.- Once the proeprty is fully under her name she's free to do with it as she pleases.

I take the opportunity to offer her our legal service on Estate Transfer to Heirs:

Estate Transfer to Heirs

This service is intended for those who are inheriting the Spanish assets of a deceased person, whether as the legal heir to an estate or by means of a will
The Estate transfer to heirs service includes

• Requesting of copies of the Death Certificate, in the event that the death took place in Spain.
• Requesting of a Will Certificate information and location from the Central Registry of Wills in Madrid.
• Obtaining of the Will from the Notary Public where it was signed / Estate Heirs Statement (in those cases where there is no will)
• Inheritance Acceptance
• Partition of the inheritance according to what the will states, or, where there is now will, to the desires of the inheritors .
• Inscription at the Land Registry of the new owners of the Estate inherited.
• Arrangement of payment of the applicable Inheritance Tax.