Was she in placebo group?
EDIT: In the original link it says the placebo group received a much lower dose, so that seems to be one way of doing it.
A difficult one with psychedelics is as-mentioned: people can easily "break the blind". But if you want to eliminate that problem you can instead do a micro vs macro dose, in which case you're measuring a slightly different thing.
I sincerely hope this is not at all how any of this works. That sounds like a recipe for paranoia.
The rest is a regular placebo. It can be a really strong thing when you are feeling hot.
This particular trial, however, allowed participants who were in the placebo group to later opt in for the real dosing - obviously with those results omitted from the trial.