Harris, 50, was sentenced to 20 years in prison for running over her philandering spouse in a hotel parking lot in 2002 after confronting him with his mistress. The lawsuit claims Harris hired Parnham for $75,000 but wound up paying more than $235,000.
Lawyers for Parnham, whose list of past clients includes Andrea Yates, have argued that Harris is the one who still owes money. "She's mad about how much he charged her," said Charles Babcock, who is representing Parnham.
Opening statements are scheduled for Wednesday in the trial, which is expected to last about a week.
Harris and Parnham never had a written agreement. Dean Blumrosen, Harris' attorney, said his client is owed between $90,000 and $135,000.
Babcock said Parnham had to take out a $90,000 loan to pay experts, consultants and others who aided in Harris' defense.
Harris' lawsuit also claims Parnham had her sign paperwork he said would help preserve her estate but was really a $300,000 promissory note and security agreement listing her homes and dental practice as collateral.
Harris repeatedly ran over David Harris, a 44-year-old orthodontist, with her Mercedes-Benz in July 2002. A jury last year ordered Clara Harris to pay $3.75 million to her former in-laws in a separate civil case.
