The grey Ford sedan pulled up at the courthouse at 9.45am. A relaxed Infanta Cristina stepped out of the car, smiling at the 10 police officers who lined her path and nodding hello to the hundreds of journalists crammed behind them.

So began Cristina de Borbón y Grecia's unprecedented court appearance as the first royal-born summoned in a criminal proceeding since the Spanish monarchy was restored in 1975. Cristina, seventh in line to the throne, was there to face six hours of questioning over her involvement in alleged money laundering and tax fraud.

The 48-year-old princess spent hours preparing for this day. Her goal was to leave the courtroom having cleared all suspicions of wrongdoing. Anything less could result in her facing criminal charges, up to six years in jail and steep fines. Four hundred miles away in Madrid, her parents, King Juan Carlos and Queen Sofia, told journalists they were watching her every move, desperately wanting to bring a close to this tumultuous chapter in the Spanish royal family's steady fall from grace.

The princess travelled to Palma de Mallorca for the day on an early morning commercial flight from Barcelona. Dressed in a simple black blazer and a white collared shirt, she was determined to show that her royal status conferred no judicial advantage.

But nothing was ordinary about this court appearance, which was conducted in private. More than 200 police officers – many of them flown in specially – stood guard, while 400 journalists on the ground elbowed each other to catch a glimpse of the action.

More than 200 protesters filled the streets, prevented by roadblocks from getting close to the courthouse entrance. Sporting shirts, scarves and even crowns in the colours of the old Spanish republic, they noisily chanted and whistled, waving homemade signs that read "Cristina, you owe me money" and "Franco or Borbón, neither were elected".

"The monarchy think we're idiots; that we should just support them no matter what they want to do," said demonstrator Pau Ribal, 25. "Yes, they played an important role in our country's history, but now it's time for them to go."

Many of the protestors carried signs supporting the judge, José Castro, who had decided to summon the infanta, praising him for taking on a corruption investigation widely seen as untouchable. "Justice has a name: Castro," read one sign. A report released this week by the European Commission showed that 63% of Spaniards feel personally affected by corruption, the highest rate in the EU.

Isidro Forteza Cortés, 70, stayed up most the night writing protest chants. "My goal is simple," he said. "I want those who are corrupt in this country to go to jail until they pay us back for every cent they've stolen."

The infanta stepped into court nearly two years to the day after her husband, Iñaki Urdangarin, first did so. He is suspected, along with a former business partner, of exploiting his royal connections to win contracts and embezzling €6m in public funds through the Instituto Nóos, a not-for-profit organisation that organised sport and tourism conferences in the Balearic islands. Some of the money was laundered, investigators allege, through a shell company that the infanta co-owned with her husband, a former Olympic handball player. Both deny any wrongdoing.

Heading into the court, lawyers from both sides of the proceedings stopped to chat with reporters. Minutes before Cristina was due to arrive, her lawyer Jesus Maria Silva, told reporters "Everything is in order. Everything is ready."

Virginia López Negrete, a lawyer for Manos Limpias, (Clean Hands) the activist group that filed a criminal complaint against the infanta, spoke eagerly of the chance to ask her questions, saying she had been looking forward to this day for years. "I'm here to represent the millions of Spaniards who want answers." She doubted whether those answers would actually come.

Her worries were confirmed hours later, when Manuel Delgado, another lawyer emerged from the courtroom during a recess and declared "the princess came very prepared to evade any questions". Cristina had said she had trusted her husband to manage their finances, he said, adding that she had replied "I don't know or I don't remember" to 95% of the questions asked.

Cristina's lawyer Miguel Roca called the day a success: "The princess demonstrated that we are all equal before the law," he said. Another member of her legal team, Jesus Maria Silva, denied claims she had been evasive, saying: "Answering yes or no is the opposite of being evasive."

Judge Castro refused to comment on the day's proceedings.

The three-year investigation has sparked public anger by shining a spotlight on the royal couple's lavish lifestyle, whether it be €15,000 spent to fly them and their four children on holiday to Brazil or €138,000 spent on furnishings for their Barcelona mansion.

For Spaniards, caught in an economic crisis that has wiped out millions of jobs and left more than 680,000 households without any source of income, the revelations have shown how out of touch the country's ruling class has become.

Spain's royals have seen their popularity plummet to record lows, with more than 40% of Spaniards telling a recent El Mundo newspaper poll that they support the idea of doing away with the monarchy. Even King Juan Carlos, once one of the world's most popular monarchs, couldn't escape unscathed – polls show more than two thirds of Spaniards think he should abdicate and hand the crown to his son.