Without the text of the specific “Human Rights Code” that you are being asked about, we cannot know for sure whether the nursery owner has violated that code. Perhaps you mean the UN's The Universal Declaration of Human Rights?
All are equal before the law and are entitled without any discrimination to equal protection of the law. All are entitled to equal protection against any discrimination in violation of this Declaration.... (UN The Universal Declaration of Human Rights)
However, it is quite clear that the owner has sexually harassed Darlene. That is not, however, the same as saying that Darlene will be able to prove her case.
One definition of discrimination is treatment of someone based on their category or class instead of on their individuality and merit. One definition of sexual harassment is requiring someone to have sexual relations with you if they want to keep their job or if they want to get promoted. This is clearly what is going on here. Mr. M does not appear, given the information we have, to have any reason to fire Darlene. She does her work well. The nursery is in its busy season. Therefore, there should be work for her. This means that her termination was surely due to her unwillingness to have a relationship with Mr. M.
The only problem here is that it is likely going to be Mr. M’s word against Darlene’s. If he did not come on to her in front of other people, she will have no witnesses to support her case.
So, there has probably been a violation of the discrimination clauses of the Human Rights Code, but this may or may not be provable. The US Equal Opportunity Commission includes sexual harassment as a category of discrimination. Cornell Law School confirms that US Employment Discrimination laws include "various types of harassment."
Discriminatory practices include bias in hiring, promotion, job assignment, termination, compensation, retaliation, and various types of harassment. (Employment Discrimination. Cornell University Law School)