Well, I can't make head nor tail of the clues themselves (though the 'ancient letter' keeps pointing me at
Miriel Th/Serinde for #4, and she could definitely be described as 'secluded'), but with three datapoints, I'm sure it's possible to deduce the password.
There are two words that come to mind as fitting the -R---IS pattern, both names: Artanis and Erendis. However, neither of them seem to fit as a linking theme. It's possible that
Erendis could be the password, making a hidden eighth name in the set; I've not been around long enough to know if that would be valid under the rules.
But assuming for a moment that neither Erendis nor Miriel are relevant, what can the three names we
do have tell us? Rose Cotton-Gamgee, Artanis, and Idril Celebrindal are all:
- Women (obviously)
- Wives (also obviously)
- Connected to a journey over the Sea (Rose's husband went, the other two made their own - Artanis twice!)
- Known by an epesse - Rosie, Galadriel, and Idril, which isn't her original Quenya name. (Clue #5 could point to this.)
- Resident in isolationist enclaves. I know, that describes half of Middle-earth, but the Shire, Lorien, and Gondolin make a good showing. (Clue #4's 'secluded' could point to this.)
- Related to a resident or guest in Imladris (ie, Sam, Celebrian, and Elrond himself).
- People whose status is in doubt in the evolving Legendarium. Not Rosie Cotton this time, but Meril-i-Turinqi, the Lady of Tol Eressëa, whose name indeed translates to Rose. Does she still exist? How did Artanis reach Middle-earth? Is Idril in Valinor with Tuor, or sleeping in the Tower of Pearl?
... it turns out three datapoints isn't enough to narrow things down in a hyper-connected setting like Middle-earth. Darn.
That '-IS' in the password really bothers me. It's just not a common word-ender in English, so my mind keeps parsing it as Elvish, which almost certainly means a name... but whose (or where's)? Other than Rivendell, there's no-one/where obviously linking Rosie to the other two - the hazard of being a Hobbit, I suppose.
... yeah, I was hoping something would have sprung out at me by this point, but no such luck. Maybe some of my ramblings will help someone else out.
hS
EDIT: They are also, weirdly enough, all credited with seeing the future: obviously Galadriel's mirror and Idril's foresight, but also Rosie's words to Sam: "They said you were dead; but I’ve been expecting you since the Spring." The Spring in question, of course, was when the Ring was destroyed; if not actual foresight, we can at least credit Rosie with an uncanny awareness of distant events... (No, probably not, but you never know!)