Mergus,
Back in the day (mostly the 1950s and 1960s) any number of large and small US firearm retailers ordered low cost box lock SxS shotguns from Spain and sold those guns here in the USA. These guns were generally well made, durable, working mans guns. Today such guns come up for sale regularly on sites like Gun Broker.
Some number of these Spanish made, US retailed, shotguns were 10 gauge guns and the gun you are considering is one such.
Lady of Spain is a model name made up by the US retailer, and it conveys no information on who made the gun or the price point to which the gun was made. To determine the maker and estimate the original price point we need good, clear, photos of the markings on the barrel flats and water table, and of the extent and type of engraving on the action.
About the only thing we can say about this gun, at the moment, is that it predates steel shot and anyone who uses steel shot in it does so at his own risk.
