From the first photo it looks pretty legit to me. Why do you guys think it's fake? If the photo was taken with the bag sitting on the orange box and dust bag would you think it's real then. As someone mentioned before you really have to see the bag in person before you can determine the bag's authentity. If unsure then take it to brand off.
If your sister feels uncomfortable buying from the seller then don't buy it. If she really wants a Lindy she has to visit the shop regularly. It's all about luck and patience, if she's desperate then buy it from brand off or Milan station.