Pending the result of the appeal, Judge Jose Castro agreed to postpone his summons for her to testify as a suspect on April 27th at his court in Palma on the Mediterranean island of Mallorca.
"Once a decision has been given on the appeal, if its content so allows, a new date will be set," he said.
The anti-corruption prosecutor said it was basing its challenge to the summons on the principle of "equality before the law", implying that the princess was being unfairly treated because of her royal rank.
"The imputation against a person of facts that, a priori, do not have criminal characteristics supposes at the least a discriminatory treatment," said the appeal lodged by the prosecutor.
The prosecutor has argued there is no evidence that the 47-year-old princess took part in any criminal act.
A spokesman for the royal palace had expressed "surprise" over the judge's decision to summon the princess, after declining to name her as a suspect in March 2012.
The royal family was in "complete agreement" with the prosecutor's decision to appeal the decision, the palace spokesman said Wednesday.
The case, which was opened at the end of 2011, is centred on allegations of embezzlement and influence peddling against Cristina's husband, former Olympic handball player Inaki Urdangarin, and his former business partner Diego Torres.
The pair are suspected of overbilling regional governments to stage sports and tourism events, and then syphoning off money to the non-profit Noos Institute, which Urdangarin chaired from 2004 to 2006.
The princess -- the seventh in line to the Spanish throne -- had seemed set to avoid being snared by the case.
But the judge said Wednesday that evidence, including emails provided to the court by her husband's former business partner, raised doubts that she really was unaware of the business operations of Noos.
The princess, who works as the director of social welfare programmes for the charitable foundation of Barcelona-based financial services group La Caixa, is accused of cooperating by allowing the lustre of her royalty to be used by Noos.
The summons is a new blow to Spain's 75-year-old monarch, recovering from surgery in March for slipped discs, his seventh operation in three years.
Though credited with steering Spain to democracy following the death of General Francisco Franco in 1975, Juan Carlos' standing has taken a hit over the corruption probe and over a luxury elephant-hunting safari he took in Africa last year at a time of record unemployment in Spain.
As part of a charm offensive, the royal household published its accounts in 2011 for the first time and lowered its budget by two percent in 2012 and by another four percent in 2013.
In addition, a palace spokesman said Friday the royal household would be included in a future law on transparency in public accounts that is now being debated by parliament.
"For two or three months since the new law on transparency was announced, we have not only said we have no objection but have requested to be included in the law," the palace spokesman said.
"This has nothing to do with what has been happening in the past few days. It is not because the princess was summoned that the royal household now is being included in the law on transparency," he added.