As for whether of not it worked the way she said; the initial tests came back positive and clearly the Vorlons were convinced enough to openly off her. Really, we have no reason to believe otherwise.
The initial tests on miracle drugs always
come back positive. 40 minutes later, they discover some cataclysmic flaw that prevents them from being used. It's just how medicine works in the future!
I'm pretty sure if the Vorlons are convinced, there's really no arguing the point.