She was released on bail pending an appeal - as were her brother and secretary who were also convicted in the case.
Three hundred police had been placed on duty around the courthouse in Bangkok to prevent trouble between Thaksin supporters and opponents.
The conviction comes after Thailand's supreme court accepted another lawsuit against the former prime minister, alleging that he gave illegal soft loans to Myanmar to benefit his telecoms firm.
Thaksin's lawyers have denied all charges, claiming they are attempts by his political opponents to discredit him.