Charlotte's gossip about Colonel Brandon and herself in Ch.20 makes me want to laugh but also feel sorry for him at the same time.
What Charlotte says is certainly not the whole story. I don't think she's lying, but I also don't think that 'Colonel Brandon would have been very glad to have [her]' or that 'he would have liked it of all things.'
I also don't think it was Mrs. Jennings who decided that Colonel Brandon was not good enough for her daughter.
I'm imagining that a great deal of pressure was brought to bear on the poor colonel, and this is the story Charlotte got when he absolutely refused. Perhaps this is even the origin of Sir John's comment in Ch. 13 "There is no persuading you to change your mind, Brandon, I know of old, when once you are determined on anything."