I can't comment on how it would help with your wife, however, I I am so sorry your family has to face this situation.
For me, a diagnosis was both freeing and confining at the same time. Let me explain.
I was 35 when I received my ASD diagnosis. Prior to that I didn't have a clue there was anything different about me. To be honest when looking back I always thought everyone was just like me. Thought like me, accepted things like me, saw things like me etc. After loosing several jobs, doing 3 degrees trying to find new things to do and a whole lot of work/life pain which ended up with me in a psychiatric ward for several months, I finally understood that all my pain was caused by Autism. This gave me a significant amount of relief. I finally had an answer and it was liberating. Unfortunately this was short lived though.
I had to get back to life, that is to say, looking after kids paying a mortgage etc, and a few years later, even with all the new knowledge and extra intervention,the same issues arise. I move on to a second job post diagnosis and guess what, 2 years later and the same issues again. The bad news is, getting a diagnosis doesn't fix the issues it causes. I now know that this is my life and every few years my traits which make me such a great employee at the beginning, just don't fly once I learn too much. I now have to live with the knowledge that nothing I do will stop this pattern from reoccurring and that is difficult to live with.
A diagnosis may help, but will not fix any issues you think it causes. There's no medication and no help unless you have lots of disposable cash to spend on therapy.
I wish you and your wife well and I hope you get through this emotionally intact.
Thanks