I think that JA had trouble with the whole Edward situation... she was really stuck for a way to make him seem less than "wrong". So that is why IMHO she had to allow a situation where Elinor not only forgives Edward for deceiving her but also is willing to consider that he might have obtained her hair surreptitiously and forgives him for that as well.

The only excuse that one can offer was that Edward was very young when he met Lucy and naieve and he had clearly fallen out of love with her... and was problaby hoping that something would happen to break off the engagement. However had he been a differetn sort of young man, he might well have gone to his mother and told her, and gotten her to buy Lucy off....