What laws would she base this on? To justify your employment decision, what factors need to be addressed? According to the U.S. Equal Employment Opportunity Commission Title VII of the Civil Rights Act of 1964 prohibits employment discrimination based on race, color, religion, sex and national origin. If this African-American candidate was denied employment based upon her race or gender, the office would be in violation of federal employment law. To protect itself, the office might wish to point to its policy that it is an Equal Opportunity Employer or demonstrate that African-American employees are present in the office, as if a pattern of discrimination in hiring and promotion on the part of the company can be demonstrated, that will add weight to the woman's case.

However, according to Nolo.com "the law does not require employers to give any explanation at all," as to why someone was not hired and it may actually behoove the office to not volunteer a reason why the candidate was not hired" ("How can I prove I was turned down due to employer discrimination?" Nolo.com. 2007).

It is more of a question of what the employee will have to prove, to demonstrate that discrimination...

For a person seeking to prove discrimination: "You may have grounds for a lawsuit only if you can get your hands on some very specific evidence -- such as memos, emails, comments, or patterns of hiring behavior -- that proves that your employer has discriminatory hiring practices" ("How can I prove I was turned down due to employer discrimination?" Nolo.com. 2007). Thus, to demonstrate this was not the case, the best move might be for the company to internally investigate what transpired during the interview and to review the woman's qualifications and resume in relation to the other candidates, to see why she would feel that she had been discriminated against, but to remain tight-lipped publicly about the process, until further evidence is revealed by her counsel.
Works Cited

How can I prove I was turned down due to employer discrimination?"

Nolo.com. 2007. 21 Mar 2007. http://www.nolo.com/article.cfm/catId/D348BE73-C552-4D58-B00586C0C0909EFA/objectId/D92FA15A-7770-4492-A29F17D1D8403561/104/150/269/QNA/

Title VII of the Civil Rights Act of 1964." The U.S. Equal Employment Opportunity Commission. 21 Mar 2007. http://www.eeoc.gov/policy/vii.html