As to the light squiggles becoming more flexible, yes this is new, Stella is getting more flexibility and variety in her control over light. I went back and forth about Grace showing surprise right then, finally settling that they are developing new stuff so fast right now that the urgent need to get to that other girl right now would overpower her surprise.

Having the feather only work if the end will turn out right seems like a cheat to me. Would you really want the feather to be a stand-in for a paternalistic deity who decides whether (and how) a person can choose to change?