Yes - there is no blame on your sister at all.

But, in the best case the suitcase is in one of many piles of luggage at airports throughout Europe and will take days/weeks to process and deliver to your sister. In the worst case the label fell off and it is never going to show up. Anyone from LH you can talk to on the phone is only going to look in the computer system (which you can do as well) - hence the speculation about where (FRA or CDG) it is.

The only thing you can do is wait, and focus on replacing the contents when they are needed.