What happens if Amazon uses the lookalike audience feature of FB? He uses the contact details of customers who was looking up the coffee machine and automatically defines a group of FB users who look alike them. In this case your wife looks alike you. Or if I would have developed the lookalike audience feature I would say she looks alike you. That is why she gets ads for the coffee machine.

[edit:] This may be considered as dodgy. In Germany it is forbidden to use the lookalike audience feature of FB and companies are fined if they admit using it.