I accepted a bunch of quests at the same time. After finding the herb women, I asked her to help cure the man who was poisoned and she told me what to get. Once I had everything, I went back to her and there was the option to get her to help start making the antidote. But I clicked on the dialog option which is to do with her stealing some keys, and once I’d done that, the option to make the antidote disappeared forever. So I probably could still make it, but I have no idea how.
This is a well known persistent bug.
It is suggested that you complete quests that involve talking to the herbalist in a different play through, there are conflicting quests.
You do not have to interact with the herbalist to make potions at all, there is a recipe book located with all the details you need to make the potion.
For all you alchemy needs I have made a detailed thread with videos (showing how to make each potion currently available to make) maps and links to threads discussing alchemy in full detail. Check it out here Alchemy Nexus (everything you need to know)
In the future please make bug reports to one of the currently existing bug threads. I know it can feel tempting to make thread for one particular subject but many of the bugs have already been reported.
Keep testing and reporting, and welcome to the forums. 
Ah thank you. Sorry, will do
If you have more issues with alchemy feel free to ask me directly or post in the Nexus.
Its my favorite aspect of the game so far so I have lots of experience with it.
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