[radagastly]

I think that, like Tom, she was beyond it's influence, though not for the same reasons. Tom was Master of his domain, and within its borders, nothing was master of him. The Ring had nothing to offer him, because he already had all he wanted and knew it. He is contentment.

Shelob was much the opposite, perhaps even a deliberate foil for Tom, of sorts (though I would never second-guess Tolkien's intentions.) Much like Ungoliant with Morgoth, her greed and hunger seemed to surpass Sauron's even at the height of his power. Surely the Ring, alone and seperate from its Master's Hand, could never tempt a creature that was already consumed with temptation. She simply wouldn't notice the difference between the Ring's poison carrots and her own lust.

Also, the Ring itself may well have held back in her presence. Certainly, Sauron had no real influence over Shelob, just a convenient truce. The Ring could certainly not expect to have any more success than that. Even if the Ring managed to take hold of Shelob, it would very likely find itself in the same kind of dark cave as it was with Gollum. Only this time, it's keeper would eat any possible finders before they ever got close enough to touch their hand on them as Bilbo did. There, on the very edge of it's homeland, it would be lost in the dark forever.