(a) That's wrong. Sections 33 and 34 of the ACL prohibit conduct that is likely to mislead the public as to the nature, the characteristics, the suitability for purpose, the quantity of particular goods or services, or the process of manufacture of particular goods.
Conduct that misleads the public as to the manufacturing process of particular goods is also prohibited. These sections appear to overlap somewhat with the provisions of s 18 and 29.
There are many ways of misleading a person. Statements can be made that lead the person hearing them to believe something that is not true. Behaving in a particular way can lead an observer of that behavior to believe something that is not true. And a failure to say or do something in circumstances where the failure leads another person to believe something that is not true can also amount to misleading conduct, particularly when, in the circumstances, there was a clear duty to act or disclose information.
In this case a customer asked for advice, and A's failure to disclose what she knew clearly amounts to misleading conduct.