If Harriet had only been available when Mr. Martin called at Mrs. Goddard's, Harriet may have been engage.
Perhaps it would have been worse though. Emma may have convinced her to retract any promise made to Robert Martin.
Most of us would prefer a marriage proposal in person. I am sorry that he did not contrive it.
I wonder why Robert Martin had not waited, or better yet, made an opportunity to apply to Harriet in person?
I think Robert Martin should have thought better.