At my best guess, and while not established fact ( I would advise you go to the World of Warcraft RP forums and find a poster who's name I forget, but is said to be in contact with Metzen himself, and answers many Lore questions), I would say that Shandris, while a child in the War of the Ancients, was placed at the head of the Sentinel army, or high up in its ranks, at its formation. Given her skill with a bow, and her continuing relationship with Tyrande (as seen in Warcraft 3), I would say that she likely chose Sardor Isle to place Feathermoon on due to it's distance from civilisation, as well as the strategically important loaction from which you can reach most of Kalimdor, (or, at least, the Kaldorei held parts) very easily.
While merely speculation, I hope this helps ; )
EDIT: Unfortunately, Xarantaur has stopped taking requests, but, here's his 32-page long archive. Maybe you'll find it in there...
http://forums.wow-europe.com/thread.html?t...=15211956&sid=1