1. "From" is the correct preposition here, because these are the notes which she TOOK AWAY FROM the class. The class which you missed is the origin of the notes - in other words, this is where they came from. Using 'in' would mean that she showed you the notes during the class. This would make no sense, as we know that you missed the class.
2. This is easy. "Decide" is an intransitive verb, so it can't usually take a direct object. If there is an object, it needs to be preceded by 'on' or 'about'.