Could you tell me if it is in any way possible to alter the names listed on the deeds of a Spanish property?

The question arises because my sister is trying to return to the UK from Spain, where she has been living with her partner (they are not married) since approx. 2004. She funded the purchase of the land and, subsequently, the building of their house on that land, in Javier. However, on working through the documentation with a view to returning to the UK (alone) she now finds that whilst she and her partner have a joint mortgage, for whatever reason, her name was left off the deeds.

She was shocked when she found this out - only recently - and realises that it was a huge and terrible 'administrative' mistake, but she trusted those involved in the purcase and just doesn't know why she was included on all other doucments, but left off what she now finds to be the key one.

She is in a terrible state, since she invested all of the money from her UK business and home into the Spanish property, and so will have lost her life's savings if the situation can't be resolved. She can also clearly demonstrate the flow of funds to buy the land/property, i.e. that the money used was hers alone.

Any advice would be invaluable.