Oh, what a horrible homecoming.
I'm so sorry.
Hindsight is always great, but anytime I had to leave pets for an extended time, I always had a back-up neighbor in case something happened to the first person we had asked to watch over things. Both neighbors had each other's phone numbers so they could communicate, and I would call to check in with them regularly. Our bird could easily be fine for a few days in between being checked due to the nature of her food and water dispensers. I left the TV on for her and she was happy. However, my elderly cat and bunnies couldn't go a day without being checked on and given fresh water, etc.
I'm not trying to make you feel worse than you already do. I'm just a worrier and for my own peace of mind, I just wanted to make sure everything was going okay.
As far as moving forward, it's going to take time. Your husband may never truly get over this. Losing a pet under natural circumstances can be hard enough. I wouldn't press him about how he feels about the neighbor. He may never forgive her. If I was the neighbor who didn't call or stop by just to make sure you'd made it home safely and your animals died or came close to it as a result, I would just want to jump right off a bridge and get it over with because I would feel so guilty. Seriously.
I would just worry for now about helping your own family through all this and worry about how things will work out (or won't) as far as your relationship with your neighbor later and/or as it comes. There may never be truly getting past this with her, that's hard to say.
Like I said, I really am sorry this happened to your family because it's tragic, to say the least. Unfortunately, there is no going back and doing things over.
How you move forward is something that you will figure out as you try to navigate it.
Just my opinion and very best wishes to your family.