I think she just said yes most times because she didn't want to go against him as PM. I think candidates sometimes find it difficult to judge when to say yes and when to just keep their opinions to themseleves. Obv there are times when a candidate says nothing intentionally to let the PM go down the drainhole with their daft idea but, sometimes they prob do just think they'll get their head bitten off and so just say whatever will make the PM feel happy (and keep him or her off their back).
I think Susan sort of agreed with Glen at times too but I just think both Edna and Susan did this because they didn't seem to have any alternative ideas themselevs to respond with. I don't think they really understood Glenn's ideas with the whole 'see their light' description' so they probably should have questioned him alot more actually. But on that task no one seemed allowed to go against Glen's idea.