Her bank accounts were frozen after an administrative ruling held her responsible for about £760,000 in losses from the subsidy.
The Bangkok trial on a charge of criminal negligence is nearing an end, with Ms Yingluck delivering her closing statement on Tuesday, and could put her in prison for 10 years if she is convicted.
“I will express to the court my confidence that I was not complicit in corruption and I confirm my innocence,” Ms Yingluck said before heading into the court.
Hundreds of her supporters outside the court shouted: “Prime minister, fight fight!”
They believe she is being persecuted by opponents of her brother, former PM Thaksin Shinawatra, who was forced out in a 2006 coup.
The telecommunications mogul was ousted after being accused of corruption and insulting the monarchy, triggering sometimes-violent battles for power between his supporters and opponents.
He has been in self-imposed exile since 2008 to escape a prison sentence for corruption. His supporters say the political establishment opposes him because his electoral popularity threatens their entrenched privileges.
On Facebook recently, Ms Yingluck said she would prove her innocence to the best of her ability because “I know that I have done nothing wrong”.
She has also been banned from political office for five years after the national assembly appointed by the military government impeached her.