To construct a strong and viable defense regarding the mortgage registered against the property at 36 Roxborough Street, West, Toronto, the following legal arguments can be made:

1. Lack of Original Contract: The enforceability of the Charge (Instrument No AT4311963) is contingent upon the presentation of the original contract. The Plaintiff's failure to provide this document undermines their claim, as the terms and conditions of the agreement cannot be verified. Without the original contract, the Defendant cannot be held to its terms.

2. Misrepresentation and Promissory Estoppel: The Defendant was led to believe that she could draw on her home equity up to 50% based on verbal assurances from representatives of Home Equity Bank (HEB). This reliance on verbal promises constitutes misrepresentation, and the Defendant should not be penalized for acting on these assurances. The Defendant can argue that HEB's actions create an expectation that should be legally recognized.

3. Unconscionability: The tactics employed by HEB, particularly in targeting vulnerable seniors, may be deemed unconscionable. The Defendant can argue that the terms of the agreement, as applied, are oppressive and exploitative, particularly given the context of the COVID-19 pandemic, which has severely limited the Defendant's ability to secure outside income. This defense highlights the ethical implications of HEB's practices.

4. Absence of Clear Terms: The Defendant should challenge the Plaintiff to produce the specific contractual clause that requires proof of outside income as a condition for accessing home equity. If such a clause does not exist, the Defendant can argue that the Plaintiff's demands are arbitrary and not supported by the original agreement.

5. Public Policy Considerations: The defense can invoke public policy arguments against predatory lending practices aimed at seniors, emphasizing the need for legal protection for vulnerable populations. This can strengthen the case against HEB's enforcement of the Charge.

By focusing on these key points, the Defendant can present a compelling argument that challenges the enforceability of the Charge and highlights the ethical concerns surrounding HEB's practices.