Everything I've read says that if a spell can potentially be used against multiple targets, it's not eligible for twinning. That's how my other GMs rule it at least.
A question:
* are cantrips in a spell book? I thought they were not. (if they are, what does it mean for casting them? possibly, scrolls could be made? I don't know).
Still to be done:
-- add two spells to book
-- make new spell selection
Ah yeah, good point. That is odd. Especially since you can't add cantrips by studying them. Might just be a quirk of the module writeup. That's a nuance of 5th Edition that's easy for vets of previous editions to miss.
Well the module says she has her spellbook with her prepared spells. I just copy and pasted (and edited) her spell selection without thinking about it in any major detail.