Justice Simon Moore ruled Thompson had "no legal or beneficial interest" in the Bonus Bonds, and the bank should remove her name as an account holder.
Thompson was employed to care for Willis in 1997 after he became wheelchair bound but continued to provide care services after her employment finished.
A few weeks before Willis died, funds which were previously held solely in his name were transferred into a Bonus Bond account in the joint names of Leslie Willis and Thompson.
In late 2000, documents were found giving Thompson authority to sign documents on Arnold Willis' behalf.
Leslie Willis found other documents, including a will which appeared to leave all of his father's estate to Thompson.
He then confronted his father who became very upset.
Willis installed a baby monitor in the house so he could monitor his father's rapidly declining health. Conversations overheard through the monitor caused him to harbour further concerns about the influence Thompson appeared to have over his father, according to the court decision.
The court heard that Arnold Willis called Thompson saying he had something he wanted her to sign. She said she went around to his house and he showed her some papers relating to the Bonus Bonds.
He allegedly told her he wanted to leave her a half share in recognition of the care she had given him over the years. Thompson said she agreed to sign the papers only because he was so insistent and because she did not want to upset him, according to the judgment.
The court ruled that the application for the repayment form and the Bonus Bonds application form were brought about by Thompson's undue influence at the time they were signed.
Arnold Willis died in September 2000.
