Spain is a member of the European Union and so may not change the application of lawful penalty after the crime has been committed, the regulation that the Supreme Court breached.
The central argument of that piece of legislation was that denying prisoners at least some hope of release was cruel and unusual punishment and likely to cause the offender to become violent and unmanageable.
Henri Parot was sentenced in 1990 to serve several thousands of years for numerous murders and offences committed, mainly for the 1987 Zaragoza Barracks bombing as a member of the armed Basque nationalist and separatist ETA, which was a designated as a terrorist organization by Spain.
He was the first person to be awarded what was effectively a life sentence beyond the statutory maximum period of imprisonment and so the term "Parot doctrine" emerged.
Spain appealed, but the European Court confirmed its decision in October 2013, demanded her immediate release and ordered the Spanish government to pay €30,000 (approximately $41,000, or £25,400) in compensation to her.