Lianne Smith, 45, had admitted smothering 11-month-old Daniel and five-year-old Rebecca at the Miramar Hotel in Lloret de Mar on the Costa Brava in May 2010.
During her trial in June her defence claimed she was 'psychiatrically disturbed'. But the jury at the Provincial Court in Girona decided she was criminally responsible for murdering the children.
The deaths happened a few days after Smith's partner, Martin Smith, was extradited to the UK on charges of sexually abusing her eldest daughter from another relationship.
He was convicted of rape and later hanged himself in prison.
Following his deportation, Smith claimed she thought British social services had arrived in Spain to take her children away from her
She told another psychiatrist she killed them "out of love" but the prosecution described the murders as "abominable".
Judge Adolfo Garcia Morales jailed her for 15 years for each of the murders.
In a written statement, the judge said that he was imposing the minimum sentence for murder because he considered that, although responsible for her actions, Smith was suffering a degree of "mental disturbance" when she committed the crimes.