My son has a girlfriend who I have never met or talked to. Her grandmother just passed away. Should I do anything like send a card or flowers?

Send flowers from you and your son.

I'd at least send a card to the family.

If you decide to send flowers, I would send them from your family to her family, not just to her.

It shows you care. That's never a bad thing.

When my Dad passed away, people I didn't even know sent us flowers - it made a difference.