Nettie is a great example of doing things really wrong: If you want the peaceful/good solution you will have to pass 2-3 checks, or kill her. These are obvious, but the good way is incredibly hard. What you might not know is that you can also use a cauldron to brew your own antidote and you can steal it from her. You might also be able to just go and get healing elsewhere.
No, the Nettie situation is an example of how we as players need to think more about our actions! Its blindingly obvious that Nettie the apprentice druid is NOT going to be able to remove our tadpoles. So why does everyone ask her to do it? Because we are conditioned to believe that we should 'do everything' in games and that we will always be successful. BG3 is NOT like that!
There is no need to ask Nettie to help us. and there are multiple options to back out before things get serious.
And there is Zero need to kill her . . . even if you fail all the rolls. There is a Knockout option in combat (why does no one ever remember this?)
Nettie ending up dead is the result of the player making multiple poor choices, not dice rolls.
Unless of course you want to kill Nettie . . which is a valid choice. The druids are in theory neutral but are acting very hostile toward outsiders. They don't exactly earn any goodwill.
Nettie will get hostile after failing the checks. If you are good you will not want to kill her, because she has a point. Talking to her also makes sense, she is the apprentice, she has additional information and might be able to help since she also studied the tadpole. There might have been recent conclusions she came to. It is logical to talk to her, if you had a disease and there was only a nurse nearby, who knows where the doctor is, you'd ask her for info as well.
Now yeah you could not knock her out, but I never got knocking out to work, the victims just died. It might only work from stealth and out of combat, I do not know, and there is noone telling you how it works. Stealing would be the optimal option, but not everyone's cup of tea.
You could use the cauldron, but there is an additional issue: When you press alt it is not highlighted, so you might totally miss it. You might as well miss the book that gives you the recipe for the antidote. Also there are roleplay reasons why you just do not rummage around in people's documents when the person is around. The game simply does not give you enough hints to make educated choices, that is why many players will just endlessly reload until they get the option they wanted, however improbable that is. That is an UI problem and a game design problem. The game funnels you into one option, partly because they created the encounter this way, partly because the game is lacking an actual relevant tutorial and partly because the UI is pisspoor and partly because their dialogue writing and conversation system is at times suboptimal.
