I agree with you that evidence is scarce. JA could have just stated that Mrs. Clay left, but JA tells us about emotions overpowering intrests. To me it was surprising to read about Mrs. Clay's emotions, because she seemed so shallow previously. Her first marriage migh have been result of stupidity, but here we read of cunning to match Mr. Elliot's. So did Mrs. Clay change or was she making the same mistake again?

Thank you for pointing out Mrs. Clay's speech about navy! She says "I have known a good deal of the profession; and besides their liberality, they are so neat and careful in all their ways! " That does sound like her husband was somehow connected to the navy. I think it would have been inappropriate and unwise to say "My husband was in the navy and he was neat and careful", but how else would she know? Is there some kind of trade where Mrs. Clay would be in such close contact?
Still analyzing your post...