Tessy has never been, and never would have been, an official member of the Luxembourg royal family. Even when they eventually did give her and her sons a title. Louis had to give up his place in the family, and they were always private citizens. They attended events like someone like Zara did.
Should Claire and Felix not be allowed to sell wine because they are using their royal status to do so? Or is it okay because Felix was born into his title. Unlike Tessy, they are actually part of the working royal family.
Tessy has a job correct. But how she chooses to support herself and her two sons in an expensive city, is her choice as a private citizen. As long as she is not bringing any embarrassment on her sons, no reason anyone should complain.
She is doing a wonderful job of supporting a number of charities. She had no obligation to, as she is a private citizen, always has been. She balances work, charity and her sons (and until recently school).