Swapping hats
Nettie's a dwarf stubborn, bullheaded, and narrow minded at the best of times. One roll wouldn't really change her mind mind, much like in 5e animal handling you have to succeed on several rolls to turn a creature from hostile, to friendly.
Having someone tell you that they may be changing into a mindflayer, in the middle of your home, and you have no way of healing them. Well your not going to be friendly to them, at most your somewhere between hostile and neutral. Then they threaten you, your home, everything you love. To a dwarf this is a biiiiig nono, put it bluntly thems fighting words, and they really don't care about your roll. So the dc goes up, again you try to intimidate them, (very hard thing to do to a dwarf their bloody stubborn, and fanatical when it comes to clan/home etc) dc goes up. If you pass these yeah you just succedded in cowing a dwarf. It may be the reason behind why that particular skill check is so hard.
1. your a danger to everyone around you. Including her, and her 'family'
2. she has no way to heal you, and yeah she feels bad about it but your noone to her, more to the point she doesn't know anything about you other then your going to change into a brain eating, mind raping entity that believes everyone is a lesser being and is either food, or slaves. The druids outside are her family, friends, loved ones.
3. The only one she knows can cure you is gone, believed to be dead, or captured.
4. She may very well be a part of the fanatics that want all outsiders gone. Your not only an outsider you just admitted your the biggest threat to the druids, because who knows what you were like b4 the tadpole, and how long it's been since you got tadpoled.
5. she believes what she is doing is right, not just for the druids, the tieflings, and their children but for you as well. (morbid but hey been done before)
So five things that maybe happening in her mind, first check sways her a little, mark off one, next check is harder meaning your going against the next harder thing, so on and so forth.
So I really again can see why the did it this way, but I can also see changing the number of rerolls or adding bonuses for each successful pass. Doing away with it all together eh not a big fan of for reasons explained above. Also again you can knock her out. Seems everyone just thinks about killing for the most part. Oh kill, kill, kill em all with fire. Cause you know dwarves are weak to fire!
