That’s lovely! I had a look at her shop. Tell your sister she needs to do a few things to finish the set-up of her shop. She needs to fill out the “About” section and, importantly, she needs to fill out the policies section so customers know what her terms and conditions are. Many people will not buy from shops that have no published policies.
If she wants to see what a fully set-up shop looks like, this is mine: https://www.etsy.com/uk/shop/FfigysDesigns
I’m happy to help her to get the set-up right if she needs assistance, she can contact me via Etsy.
Furthermore, I’ve just spotted a problem that she needs to fix ASAP. She charges a fee for delivery within UK (absolutely fine) but she has international shipping listed as being free - that’s a HUGE error that needs fixing as it could be very expensive! Edited to add: I checked another listing and that one said it didn’t ship to US so the one I spotted may be the only one with free international shipping, but she should check them all to make sure.