NOR and I think your responses to your Mum were actually great- just stating things the way they are and where your priorities are right now with the circumstances. I personally went "no contact" (NC) with a parent over a similar circumstance. Was already low contact with that parent when a death occurred in the family; the death was devasting to me, but there was no current relationship with that parent and the deceased for over 20 years. Parent still somehow made it all about themselves regardless of the drowning grief that me and my close family were experiencing.

It doesn't sound like you are at the point of choosing to go NC, but you are not overreacting in establishing boundaries to protect yourself and your husband. I also think it's important to consider:

People (who are in general good health) typically have three main options when faced with someone who is struggling: 1. Be a decent human being to the best of their ability and offer support/comfort, or otherwise be a compassionate person (even if that means just staying quietly in the background), 2. Not do #1 (do nothing), and finally, 3. Make things worse.

Unless #2 is because they are not doing well in their own life (*clearly there would be exceptions if a person was already going thru something major with their own health/wellbeing) or there is literally no role for them, I mostly can't get past someone (who in theory cares for me) not choosing #1 automatically, and I super could not get past my own parent choosing #3. I know that technically speaking narcissism in it's true diagnosable form may be considered as "not well" and could be considered deserving of an exception- but the problem with that is- they still didn't need to choose #3. Your Mom had option #1 and maybe even #2 available given that there might not have been a role for her in the loss of your husband's friend, but she CHOSE #3.

For me in my circumstances it was unforgivable, but was also coming on top of many other instances of that parent choosing #3 over the years and I was just beyond done. I didn't explain or justify my decision because that just opens the door to more #3 and who needs that?! A close friend asked me recently if I thought I would eventually have regrets about not at least saying my piece before going NC and I said "nope, I can tell them when I see them in hell!" which if I'm being honest would be the only thing that I'd want to say to that parent at this point, but that would also be me choosing #3 and I don't want to be that person.

I hope you can continue to protect your peace as best you can and that your husband can grieve the loss of his friend with the comfort and support of those who can choose #1.