Do you stay broken from the poison?
The issue is that the Druid is the one suffering from poison. The rules on removing poison are very vague and unclear. Will she 'unbreak' by resting but die later? Can she be unbroken by the Bard with his Hymn of X so she can wake up long enough to attempt to heal herself? If she can unbreak, she could attempt to heal herself with a spell. If she lingers broken then she'll basically die (as they have already used the one antidote they bought earlier in the week).
Edit: Nevermind, it actually says you stay unconscious until healed or death.
So, I guess that character is dead then.
I would use characters survival or lore. Make them see if they know a remedy (be forgiving). Spend quarters of a day scouring the wilderness for things to make an antidote. Use cooking to boil leaves/roots/whatever. Hope they have enough time to put it all together while that d6 days clock is ticking. Spend a water resource every 1/4 day from which ever party member is watching the poisoned character while they try to keep them hydrated.
The issue is while poisoned the character cannot recover strength. They cannot become unbroken because the poison will not let them. While poisoned you cannot recover strength if I remember correctly).. Once the poison breaks them consider them to be rolling around in fever dreams and pain until the poison finally takes them. Be dramatic about it.
A remedy made this way 1) Doesn't last. It has no shelf life. They cannot stock up on it. Thats why you BUY antidotes. 2) they need to gather a lot to make very little. Put them through a lot to walk away with only a single dose. 3) Maybe don't have the wilderness manufactures remedy work like an antidote and automatically work. Instead have a character use heal/medicine (whichever it's called. So... use the successes of the cooking roll used to make it as the remedy's potency (how many dice it will add). Have the person who administers it make a heal/medicine roll (# of successes get added to the next roll) and finally the poisoned character (who as no strength) makes an endurance roll with a bonus equal to the remedy potency + the successes of the heal/medicine.
If the character cannot pass that check... it's done. Dead.