Well that is very strange. It seems like we have two issues here. . How did it get there, does she keep it, and 2. Is it real.
I think her explanation of how it got priced at Target is likely. Maybe to quell her conscience she should go back to that target and ask if anyone reported a missing Hermés scarf. If so, find the right owner, if not. Take good care of that and appreciate it as a special gift from the fairy fashion godmother.
As for the authenticity there are a few points to consider...fakes generally do not have the same exact print as the real ones. For instance, I have an Hermés scarf with keys, the real one has 72, the fakes out there only have 46 keys. So explorer the photos here and see if her scarf has the right amount of bugs, monkeys, mermaids, etc.
This scarf also has the artists name hidden in the print. Not all real scarves have this, but it is one more point to look for. Hermés Paris should also be printed, some times twice, on every scarf. The appearance of the accent over the e, and the copyright symbol can also have date the piece. And lastly, the white corner hang tag. These have been known to fall off, but if it is there, and if it says some thing other than may add to the authenticity of it. I recently had a 1977 Hermés scarf in the store that had a Neiman Marcus tag attached next to the white Hermés one, another variation on what to look for depending on the age.
So now we have an expert opinion. Change your mind from Monday? Would you keep the scarf you bought for $14.99? Would you check in with the store? Would you even have bought it in the first place?