The law doesn't enforce ethics--only legal or contractual duties. And it does not address "conflicts of interest" in terms of a person in a business wearing more "hats" (having more or conflicting responsibilities) than she should. Legally, she did nothing wrong: if she believes an employee may be using drgs, she can discuss that with other employees to see if they can corroborate it and she can have the suspect employee be drug tested. What she did may be improper in some way, but there is no legal recourse for you, unfortunately.