As long as Bob has Cursed Totem ("Players cannot play any creature abilities requiring an activation cost.") in play, Sue can't use the ability of her Llanowar Elves (": Add to your mana pool. Play this ability as a mana source."). This is because Cursed Totem stops creature abilities requiring an activation cost from being played at all, rather than countering them once they've been played.
: Add 
to your mana pool. Play this ability as a mana source."). This is because Cursed Totem stops creature abilities requiring an activation cost from being played at all, rather than countering them once they've been played.