I've always thought that Charlotte had a real blind spot if she thought that Lizzy marrying Darcy would mean another living for her husband, when she reflected at the end of Chapter 32 that on balance she preferred Lizzy to marry Darcy rather than his cousin, because Darcy had "considerable patronage in the church, and his cousin could have none at all." Charlotte has a realistic picture of her husband, and she knows Lizzy's opinion of him. What would make her think that there is any chance of her husband getting one of those livings?

It has occurred to me that there is no mention of Mr. Collins, just a general reference to livings. Could it be that Charlotte isn't thinking of another living for her husband but rather that she's thinking ahead to a time when a younger son might need a living? Given her own experience and her knowlege of her world, Charlotte must know that a younger son can be in a precarious position. And after all, livings were granted for life, and so they didn't fall vacant every year. It could be many years before one of the livings that Darcy had in his gift was available.