Both Ellie and Ruby are curious. Both of them are away from their real home.
In all honesty, if those are the only traits they have in common, then it's unlikely that anyone is going to notice any similarity at all. Certainly, this isn't anywhere near enough for you to get in any sort of trouble if you were to publish your book.
If your protagonist was also ...
Possibly a good idea for a writer who wants to write Arthurian stories is to start reading them from the earliest writings onward and note which plot points are out of copyright.
You could start by reading about the possibly historical Arthur in the Historia Brittonum and the Annales Cambriae.
Then try reading early Welsh Arthurian stories and poems like &...
The Arthurian legends are in the public domain. You can use the names, places and storylines as much as you want.
To quote this Quora source:
Sure you can. Camelot, King Arthur, the Holy Grail and the Round Table
are all in the public domain. You can use as much or as little of any
of them as you like in whatever story you want to tell. No-one is
going to ...
Names are not copyrighted. However, some can be trademarked.
To clarify what that means:
a copyright fully protects an entire work of authorship, i.e. a book, movie or work of art.
a trademark represents a specific part of your brand or product, and is usually used for names, slogans or logos. (Source)
So you cannot legally "copyright" a name, ...