Sometimes nannies lose touch with their employers, or they may have left under a cloud and not feel comfortable relying on that as a standalone reference. To stop it being a case of their word against hers, nannies will probably give you contact details of someone who can corroborate their story.
If they were placed by a nanny agency the agency should at least have a record of the placement date, and whether they received any complaints about the nanny. Bearing in mind that agencies do have to respect their client’s privacy you may not be able to find out the finer details but it should be enough to help you decide whether the nanny is telling the truth or whether they are trying to cover something up. Equally a nanny will frequently turn to the agency that placed them when they encounter difficulties. Ask the agency direct questions: ‘did this employer ever raise any concerns about this nanny with you?’ or ‘did the nanny ever come to you for advice on dealing with problems with these employers?’. However, the agency is unlikely to have had substantial involvement so they may also only have the nanny’s word to go on.
A private placement is more problematic. The nanny may have kept in touch with friends or teachers from that job, especially if it’s more recent, but again they’re only likely to have heard one side of the story. Where a reference comes back very negative and the nanny insists that their ex-boss is being unfair you might want to know whether they’d complained about it at the time. Your prospective nanny may have consulted external organisations such as their insurance provider or a professional association, or sent emails detailing their side of the story. It’s not foolproof but seeing this kind of evidence may help you make up your mind.
A solid employment history is very important for nannies, and both employers and nannies tend to appreciate that, so will make efforts to maintain contact and at least civil if not cordial relations. At least by offering an explanation a nanny is demonstrating that they understand how important it is and avoiding a large unexplained gap which may set alarm bells ringing.