I love the photo idea if you happen to have any.
I've unfortunately lost several friends who lived quite a distance from me, and was unable (or unwilling) to head to the funeral. What I've done in the past is to get a gift-card to a local take/out delivery restaurant and tuck it in the card to the family. Food they don't have to cook, and won't go bad. (Ahem, I've also sent scotch in the mail...but that's one of those dicey things, in how appropriate it would be considered). While your friend *may* have wished her ex dead at least a few times, she's still likely to be having a hard time, both for herself and definitely for her son. Not having to cook at least a night or two might be a godsend. Very few people think of the ex in these circumstances. Even if the ex is dealing with a grief wracked child 24/7.
For a different friend who was killed and who had children, several of us opened up a college savings acct. for friends/family to donate money into. Anyone can DEPOSIT money into any acct after all. The bank helped us set it up. In this case there was no life insurance payout, although his estate/will DID cover funeral expenses, child support and alimony was *poof* gone.
My condolences, and best wishes
R