I think the way you "uninvited" her was very rude. And, frankly, very unkind.
You don't like her, but there is no need to be so nasty- it's not just the rescinding of the invite, it's your general attitude of "needs to get her own life"- well she's trying to make friends after a major life event. She is trying to do this via her good friend- who happens to be your DH.
I can see why you might be upset that he cancelled on you- although I might cancel if my friend was really upset and needed support too. You were hurt by it- did you tell him? Or quietly seethe at her and not bother to say anything to your DH?
It seems your DH and this woman are good friends- she supported him through a tough time and they became close (you seem to think more than "just friends" close though- and I think this is the heart of the issue). Now he is supporting her through a tough time. Your DH is being a good friend, by the sounds of it. Do you think there's more to it, and that's your problem with her? If so- you need to speak to your DH about it, rather than take it out on this woman.
If you have a problem with your DH being friends with this woman, you need to come out and say so, and explain why. Although, I don't think you have any right to dictate who he can be friends with unless you have a very good reason (and more than a "hunch").
Yes, your DH should probably have asked before inviting (although I wouldn't have minded unless you had a specific arrangement with this couple that it would only be you for some reason). However, for you to cancel in that manner and without telling him, was unreasonable. You
I find this "couples night" so nobody else can come very odd. Can't couples be friends with and socialise with single people?
I think your DH may now be as pissed off with you as you were with him- you're as bad as each other. Playing tit-for-tat with other people isn't nice.