On the other hand, were Mrs Bennet somewhat more sensible, she may not have started off by assuming that Mr Bennet viewed the matter like she did. And therefore she may not have irritated him so much, and they both might have been happier.

As for Mrs Bennet telling Mr Collins her opinion, from JA's description she seems to have blurted it out:
This information, however, startled Mrs. Bennet;... she dared not to believe it, and could not help saying so. (chpt 20).