Wait, so, despite her stealth being passive, ANY nearby champion can see her? That's what I'm getting from that description.
That's it. The idea is that, to the enemy team, she'll be constantly MIA, until she approaches and attacks an enemy champ. Or farms minions, for that matter.
That seems more useless than her regular stealth, since now you don't even need wards or oracles to avoid ganks by her. Unless it's super short range where they can see her. That's probably what it will be, because if it's like regular oracles distance, it seems a little useless to me.