That a two year old will back isn't surprising. It certainly doesn't show any natural ability. Below are three four month old pups. None has ever been on a check cord, worked on a planted bird, nor worn an e collar. The picture was taken about six weeks ago or so.
The lead pup is the only one that could have possibly smelled or seen a bird, the other two are "backing naturally". This isn't something amazing, it's pretty common with well bred GSP's.
I'm not saying that there's anything wrong with the bitch, but you are being sold a bill of goods, or a steaming shovel full as to this wonderful "natural backing at the age of two". By the time dogs get to the SR test level (lots of dogs can pass a SH test at 2) or adult field trial stakes (which starts at the age of two) backing is an absolute requirement, not something seen as "special".