Spoilers for Act 3
The bit of text about Ethel offering an out surprises me: I’ve done that fight around eight times and she has never once offered me the option.
In the first Ethel fight you need to let her take her turn when she’s at like, 10-15% HP and she’ll offer to give you power (+1 to any stat) if you let her and Mayrina go. If you pass a high intimidate or deception roll you can save Mayrina and get the buff. (Warning though: doing this breaks paladin oath if you care)
Nope, just a straight +1 to any stat. You have to eat a gross magic piece of her scalp though to get it
And for anyone who wants to cheat it on a paladin just make sure someone else is closer to Ethel than your paladin. Doesn’t count as breaking your oath if someone else does the conniving. Also she starts the conversation with the closest person. Make sure you change the auto select character after combat to off in settings or this will all have been for naught.