I have followed your ordeal from the beginning...and I still can not express how much my heart goes out to you all!
I do think, like you said, Maddie needs to stay w/ the couple next door. That poor girl has been through so much...and it is wonderful for you to think of others before yourself (especially that precious girl). It sounds like she has found a wonderful place and has enriched the lives of her new owners in so many ways...and a plus...she is just next door. And it sounds like you all have a great relationship w/ each other....so, I think that is an easy choice. (a win-win for you all).
I do not know what to think about you getting another Yorkie right now. I mean, your daughter just has started w/ the shots...what if something else happens and you have to rehome another baby? I mean, what would that do to you all again? I would hate to see that happen. I would wait...give it some time....
These are just my thoughts/concerns/opinions....and no one knows what is best for you and your family....other than yourself. Just know....you and your family are in our thoughts and prayers.