Why not keeping it as Selkies? It wouldn't be the first mythical creature that artists (writers are artits too) reinvent/create new identity for. As an exemple, like how ugly and terrifing vampires became pretty good? Or how J. R. R. Tolkien reinvented the elves as the proud creature we now know of.
No, I love how you call the them Selkies. That's pretty much how I know you for is calling them Selkies. And it's such a beautiful name. Nohtseuhls just looks hideous (I hope you don't mind me saying) and not as creative as Selkies. I personally think you should keep the name you have and don't change it. You don't need to stop calling them Selkies just because people say that's not what they're called. Who cares? It's unique and to me it sounds perfect for how you draw them.
Well technically "Selkies" are already a mythical creature, people on land but seals in the sea (sometimes when they talk they can enchant humans into doing whatever they want). Maybe she's trying to break away from that and be more unique? I love how she draws them, too, but luckily the name won't change that.