This is the correct answer. If Nettie is very, very hard to persuade, make it a DC 25 check.
There is another one in the game, I think with the zhentarim lookout, that is DC 25 - AND IT SHOULD BE, you don't have the password! Sometimes people are very very hard to convince
What would be BETTER is to make it a skill challenge!
This would be the *PERFECT* time to bring your companions in! A skill challenge with you and two companions of your choice getting a check suited to their character. You need to get more successes than failures. That's how to do multiple rolls
Main Character [Persuasion]: Please don't do this, you don't know I'm going to become an Illithid. I deserve a chance to find a cure.
Shadowheart: [Religion]: Sylvanus wouldn't approve of you murdering me because I MIGHT become dangerous, that's the kind of "What if" thinking that human civilization uses to justify any atrocity
Gale [Arcana]: I would have symptoms already if this was a normal tadpole, and I don't, clearly you're lashing out at a thing you don't understand
Lae'zel [Strength* Intimidation]: Try it. I will gut you like a wounded neogi, plantspeaker.
Bingo, this.
You WOULD need to account for a party of entirely custom characters, and multiplayer, but that could be done if the game checks your party for high proficiencies in areas.
