Considering nobody here actually knows what any of these untested substances (sorry, Substances) do, that's just completely untested and probably factually incorrect?
She's almost certainly being hazed, but on the other hand: if this dumb prank sends her to the hospital, maybe someone there will actually help her with her weird brain problem. Which is ultimately what she wants. This is incredibly stupid, but also, it's her literal job, none of the plants she was picking were poisonous, and a food serum would probably be great for reducing world hunger. Also, if this is a prank and she just plays it absolutely seriously, all of her coworkers will be slightly terrified of her, which sounds like great fun. Also, like, she ate the heirloom fruitcake, so clearly she's a crazy person.
So that's why she picks out the Substance that looks like it's done some sort of something or other - that is, not one of the ones that just looks like bits of flower petals in water, and not any of the unappetizing looking brown ones - and then: well, bottoms up. If this does terrible things to her digestive system, she's pretty sure she's going to be set for life, insurance wise.
Glug!