IF the coworkers are provably lying, then they may be committing defamation, and your wife may have grounds to sue them. Defamation is the making to others of an untrue factual statement which damages a person's reputation. Opinions are not defamation, however, so saying that your wife is "not doing her job" may not be defamation, since whether someone is "doing her job" or not is an opinion. But a factual mistatement could be defamation. So if instead of saying "Jane Doe is not doing her job"--which is an opinion--they say "Jane Doe comes in late, takes a long lunch, and leaves early," which are factual statements, if those statements  are untrue, that could be defamation.It is the coworkers themselves--the ones making the statements--which your wife may have a cause of action against, not the company, which is the recipient but not originator of the statements.