Wilona was married to Wilbur for 40 years. She was devastated when he passed away. She had been very reliant on him and left all their business matters to him. She had always been a religious person and turned to her faith for solace.

She was visited by her local priest, Father Devout. She talked about her situation with him and concluded that she should sell her matrimonial home and move into a small unit. Father Devout was himself looking for a new home after the church had informed him that it would be selling the bungalow adjacent to the church building in which he currently lived as a cost- cutting exercise. He mentioned this fact in passing and Wilona insisted that she sell her house to him. When he asked how much she would want for the property, she said she had no idea of its worth. However, she had heard a neighbour say that a house in the street had sold for about $200,000, but, because she knew that her house would go to someone deserving, she would sell it to him for $100,000. This was in fact half its true value. She wouldn't take no for an answer and Father Devout knew her to be someone who would obstinately insist on something once her mind was made up.

Wilona needed a bridging loan to purchase her unit. She does not trust banks and instead approached Sly, a fellow parishioner. Sly was a wealthy businessman, who told her he would give her the necessary funds if she signed a receipt for it so he 'would have something to show the taxman'. In fact, the "receipt" was a basically-worded loan document, which provided that she was liable for interest at twice the rate that she could have obtained from a bank. Wilona signed the document without reading it because she thought Sly, as a fellow churchgoer, was "a good man".

Wilona's son and daughter have just flown in from their respective homes overseas and discovered what Wilona has been doing. They seek your advice on whether she can undo what she has done.

Advise Wilona's children, discussing all available grounds for relief under Australian contract law.

Please support your answer by relevant principles of Australian law and cases decided by Australian courts (preferably the High Court) and/or scholarly articles. A minimum of 3 genuine and relevant references.

NOTE - Please be informed this is normal question and answer and not an assignment.