Pichit Chuenban, a lawyer for Ms Yingluck, said after the Office of the Attorney-General (OAG) decision that Pheu Thai had evidence that was being sought by the OAG which would defend the former premier's position. The evidence was thrown out by the National Anti-Corruption Commission (NACC), he added.
The OAG refused to accept a recommendation of graft charges against Ms Yingluck for corruption in the scheme by the anti-graft office and spelled out three points that needed clarification, including more witnesses to substantiate the NACC accusations.
Mr Pichit said Pheu Thai was convinced that additional witnesses would give the party more weight in the fight against the allegations.
"We are ready both in witnesses and documents to prove that Ms Yingluck is not guilty as accused by the NACC and the Democrat Party," he said.
The OAG and NACC will set up a joint panel to work on the case to complete the probe before making further decisions. Members of the working committee will be named in 14 days.
The Democrats took the case to the NACC.
Acting Pheu Thai spokesman Prompong Nopparit said he hoped for fairness from the joint body looking into the case.
Pheu Thai was at odds with the NACC when it was investigating the allegations. The party accused the graft busters of a lack of neutrality, while the NACC said Pheu Thai was using tactics to delay its work, including proposing unnecessary witnesses to testify on Ms Yingluck's behalf.
The NACC investigation concluded that Ms Yingluck could not evade responsibility for the damage caused by the scheme as she had chaired the National Rice Policy Committee. Pledging rice for farmers was a flagship policy of Pheu Thai and promised to voters in the 2011 general election.