Because obviously the players will all want to encounter a version of Shelob that their characters can fend off. Besides, if you don’t put that NPC in one of the game sessions the party will come up with an excuse to steer the campaign in her direction anyway. The real question is: do you let the party gack Shelob early? I mean, sure, you can just say “that was her twin sister Lazy-Lob, and she would have been ten times worse than Shelob! Well done!”
But that seems a bit too pat.
Moe Lane
PS: I swear to God, this particular lens does wonders to make me tolerate RINGS OF POWER.