Mato is in the dock as part of the so-called Gurtel case, which centers on a vast network that allegedly saw companies shower lawmakers and civil servants from the ruling Popular Party (PP) with bribes in exchange for contracts.
Altogether, 37 defendants face justice including two former party treasurers and businessman Francisco Correa, the alleged head of the network.
Mato, who was forced to resign in November 2014 over the scandal, is accused of benefiting from presents made to her ex-husband Jesus Sepulveda – also in the dock – when he was mayor of Pozuelo de Alarcon near Madrid in exchange for alleged contracts.
Prosecutors said people involved in the corruption network gave trips and luxury items to the couple between 2001 and 2005, and paid for birthday or communion parties for their children.
They estimate that all in all, Mato benefited from more than €28,000 ($30,000).
Her husband risks prison for embezzlement of public funds and influence-peddling but Mato herself faces no criminal charges.
On the stand, Mato maintained that she did not know how three high-end cars in the couple's garage had been paid for.
“Mr Sepulveda,” as she referred to her ex-husband, “was in charge of family trips and the decoration of the children's parties,” she said, adding once again that she had no idea how these were financed.
The prosecutor retorted that she had responded “in quite an evasive manner” to questions.
Mato is suspected only of having benefitted from illegal funds – not of having actively participated in anything – and as such faces no criminal charges.
She could, however, be found to have civil liability and be ordered to pay back that money.
The PP itself has also been called to the stand via a legal representative for allegedly benefiting from funds obtained illegally by officials through the corruption network run by Correa, a surname that means belt in Spanish, or “Gürtel” in German.
Like Mato, the party faces no criminal charges, and it refused to testify and answer questions on Monday, as is allowed under Spanish law.