Well just like other people here have highlighted, not only traditional banks charge for your taxes, centralized exchanges also charge for your taxes based on your jurisdiction as tax laws actually differ across regions. However the thing is most people don't bother to read through the rules and regulations during sign up so they may not be aware those fees collected by the exchange does have your tax in it.

This depends on your region like I said initially plus they would ask how she got the funds something like a proof of ownership ( which is basically why centralization is messed up.)