You could also try using NFT Showroom here on the Hive blockchain. You still need to be whitelisted as an artist to begin posting your artwork, but it is a smaller community where she may get relatively more exposure given that there are still less than 1,000 artists whitelisted as of right now. At the moment, it costs 5 hive to mint a first addition of a piece and 1 hive for each additional edition, which is much cheaper than most other platforms as far as I am aware. Here's a link to a page with instructions for how to apply as an artist: https://nftshowroom.com/get-started

Best of luck! Hope you find something that works.