Hawk
Just want to offer my condolences and say what everyone else has said.
I know its these situations that make you feel on the outside looking in and marginalised but you have offered support, which is all you can do.
When I lost my parents I remember reading some things on a discussion board of people in the same boat but who, unlike me, had bad childhoods and their parents were not kind, loving and caring, like mine were.
In a way their grief was worse because instead of having 'straight forward' grieving thoughts, it brought other things to the surface too, like anger at the person, sadness for the relationship that never was. etc.
I am sure your wife and her family are going through all of this and it is a sad but confusing time for them because of the life your SIL lead.
I am also sure if she needs you she will reach out to you and if she doesn't now she might later.
You can always check how things are for your daughter..... but you have shown kindness and compassion and that will be remembered.
As far as OM is concerned, try not to give him headspace. In no shape or form can he offer the same support you would have been able too or can because he hasn't the history, knowledge of your SIL, family dynamics etci and it is at times like this these things are so meaningful, because you don't want to explain the background you just want to share thoughts and stories of the person.
"I can't go back to yesterday I was a different person then"..............Alice in Wonderland
you NEVER know how strong you are, until being strong is the ONLY choice you have"