Law of contract

Betty is a registered moneylender and she has lent a considerable sum of money to Bobby to finance his share brokerage business. Owing to several defaults of Bobby's clientele to meet their obligations, Bobby is in serious financial difficulties. He is unable to repay his debts, including the loans due to Betty. There are rumours that Bobby may be planning to abscond. Betty quickly approaches Bobby and an agreement is reached between them whereby Betty agrees to accept 30% of the loan as full and final payment. Bobby pays her the next day. However, owing to the upswing of electronic technology related company shares, Bobby, on selling his shares, is suddenly flush with cash. Betty hears about his good fortune and demands repayment of the balance of the loan. Bob is unwilling to meet her demand.

Advise Betty Pang of her legal remedies, if any.