Pay someone who knows how to do it to do it. I'd assume Shopify would be the way to go, but there are probably alternatives. Assuming she already has a credit card merchant account, she'll probably just need an authorize.net account and be ready to go.

If she's got unique items, I'd consider the "fulfilled by amazon" service. You send them your stuff, and they ship it out when someone orders it. (maybe this is just my amazon prime addiction speaking)