I'm sitting here trying not to fall off my chair.... LOL
First of all, there is no such thing.
Second of all I think your sister should find a different LQS to shop.
There is NOTHING special about a lefty sewing anything - other than 'we' do it left handed. Sure there are lefty sissors but EVERYTHING else is the same for a lefty as it is for a righty. All the tools are the same (other than possibly sissors) and we may lay out / cut our fabric from a different angle but the end result is still the same.
What your sister's LQS said is, in my mind, equivalent to saying a lefty needs a left handed iron. Pooh! An iron is an iron. Thread is thread.
Tell your sister to find another place to shop.
LOL
Shari