The herb only makes you invincible to the virus for ONCE, it was briefly explained in the early chapter. Because it mentioned the word "once", I assume once you get bitten, the herb works right away and it's not a permanent thing. Which is if you already survived the bite once with that herb, the second you eat the herb, it won't work anymore. So she probably save it for the later.
that wouldnt make sense. do long as she eats it, its for the first time she gets bitten. it doesnt matter if the first time she gets bit is a year after she took the herb - so long as she has taken in shes immune to the infection at least once. there is zero purpose in waiting to eat it.
i say she either wants to give it to her brother, or, since she plans on planting it she has to wait until she has a successful harvest before consuming one herself.
I don't understand why she isnt eating the herb that can stop people from turning into monsters. Yes she can't save everyone, but why isnt she giving it to people she wants to save atleast?
Does it need it grow more or something