I'm only casually into LOTR, but I immediately recognized her name from my beloved copy of the Dragonlance Atlas. Quite fun to read how she basically invented the field of professional fantasy cartography.
I'm a huge fan of Tolkien, and I had never heard of her. How bizarre. I wonder if she is mostly well known in America or whether I simply managed to miss her work. I am very tempted to get "The Atlas of Middle-earth" now though.
She was more well known longer ago when there was less material. Probably a lot of her stuff has been remixed and reused the original authorship has been forgotten.
More recently (>2000), I believe it's become apparent there are quite a few errors. Little things like rivers misnamed or roads or rivers mixed up. It's an accomplishment nonetheless and was a big deal when a Tolkien fanship was more niche.