I have reproduced below Annabella's list  together with Lady Melbourne's written comments in response.
He must have consistent principles of duty, governing strong & generous feelings, and reducing them under the commands of Reason.[Lady Melbourne:]
this is altogether too generally express'd - & consistent principles of duty not strong enough - As Man should have strong fixed principles of duty - generous feelings are absolutely requisite, but once having strong fixed principles, & generous feelings it is unnecessary to say, that they must be under ye command of Reason, the having them implies that -[Annabella:]
Genius is not in my opinion necessary thought desirable if united with what I have just mentioned.[Lady Melbourne:]
Genius certainly not necessary, but very agreeable, as it serves to lighten the Weight, and sometimes dullness, that is often attendant, upon good sense & reason when not join'd to cheerfulness & other pleasant qualities.-
I require a freedom from Suspicion & from habitual ill humour also an equal tenor of affection towards me, not that violent attachment which is susceptible of sudden increase or diminution from trifles.
whether ye Husband is suspicious of you or not, must in a great degree depend upon yourself - if your conduct is fair & open, nobody can Suspect you, unless he should have a very bad temper which of course you must
can deceive you on that point if you should have even a Slight acquaintance an equal tenor of affection without any variation, would be very tiresome, & and cannot be expected, no person's manner can be always exactly ye same, altho' their affection may remain unalter'd that is ye point to look to -[Annabella:]
I wish to considered by my Husband as a reasonable adviser, not as a guide on whom he would implicitly depend[Lady Melbourne:]
Whoever you may marry will look upon you as ye fist I have no doubt as for the second you need have no fears.[Annabella:]
So much for ye chief requisites of mind, & for ye sake of these I could enought to enable to continue without embarrassment in the king of society to which I have been accustomed - I have no inclination to extravagance; and should be content to practise economy for ye attainment of this object.[Lady Melbourne:]
let us consider that these chief requisites are when stated together - consistent principles of an even sort of liking for you. I would you leave out good nature & cheerfulness - of without ye first every other quality may be disagreeable let them be ever so worthy of admiration; the second renders everything pleasant.
A man in this case has your free leave to be obstinate perverse morose sulky and ill natured - the great requisites to me would be good Sense, good Nature and cheerfulness The first aided by the second must combined every sort of good feeling - & the third added to them must produce amiability - & surely that is ye sort of Man with whom you may hope to pass your life happily, & whom upon procuring the other sthan look for trifling perfections while ye greater & more amiable feelings are left unexplored I mean particularly good nature which I look upon to be the most essential requisite for for any person with whom you are to pass your Life- The rest as to fortune &c I approve[Annabella:]
Rank is indifferent to me- good connections I think have an important advantage.[Lady Melbourne:]
The rank of any person you would marry would entitled you to make good as well as agreeable connections.- often when you are obliged to live with the family, into which you marry, it may be very unpleasant.[Annabella:]
I do not regard beauty, but one could attract me- but am influenced by the manners of a gentleman, without which I scarcely think that any one could attract me.[Lady Melbourne:]
a good looking Man is often to the manner of a Gentleman without which no person can be agreeable or ought to be tolerated with a view of making him ye Husband.[Annabella:]
I would not enter into a family where there was a strong tendency to insanity.[Lady Melbourne:]
This I think is a very wise determination, as it may prevent a thousand disagreeable occurrences you might be liable toOn ye whole it appears to me that it is almost impossible while you remain on the Stilts on which you have mounted, ye you should ever find a person worthy to be ye Husband. As you are determined to look only for Sterling worthy & make it a point to yield to no Amiable qualities, you will never yield at all, for the first without ye assistance of the Second, are not captivating - a Man possessed of Such a Character as you have drawn would marry you from reason, & not from Love - which you will not say is that you would wisht or like.
Marriage after all we can say, or do, must be a sort of Lottery, I do not mean by this to advise any one, to give away to an Attachment, hastily or lightly, As much care should be taken as possibile & no pains spared to ascertain ye Character of ye person,- but yet deceit may be practiced, & ye very qualities you describe are ye easiest to be assumed- anyone can pretend to have ye best principles They need only read the part of Joseph Surface they may also pretend to Strong feelings, & ill humour may be disguised, that however is ye most difficult but good nature, openness frankness generosity; kind of heart - these can not be mistaken if you have any opportunity to judging, such as you would have in those circumstances.
1. Byron's "Corbeau Blanc": The Life and Letters of Lady Melbourne, 1751-1818
Jonathan David Gross (Texas A&M University Press, 1997)