I'm afraid these have a bit of a reputation for being unreliable - a major UK importer is forever listing "faulty" ones on eBay at reduced prices, so they must get quite a lot either returned or simply not working when tested before sale.
You mention having tried everything, so I won't ask stupid questions about batteries in the handset..... I would suspect a faulty transmitter handset.
You say your Wife bought it as a second-hand item - was it a physical cash purchase somewhere like a car boot sale, or online? If it was bought online then you should have some sort of recourse from the seller, if it was described as working.....?
If you can't get it working, then depending on how much was paid for it then it might be worth stripping out the RC gear and replacing it with a simple "proper" RC setup from someone like our own PhilP on here, or some Fosworks gear as JonD has been putting in some of his locos recently - have a quick trawl through the "Battery power" threads for somne ideas.
Jon.