I think it's quite a tricky thing to mark, in a way that's not potentially overstepping, if you're not one of the bereaved friends and relations.
I know some people remember and - not celebrate, but I can't think of the right word - anniversaries of loved one's deaths, but I'm someone who doesn't. I think it's quite a risky thing to do on the first anniversary unless she has other anniversaries that you know she marks in some way.
I actually don't know the dates of death of my loved ones who have died, and I would be very off put by someone remembering and sending me flowers. It would feel intrusive and a bit like they'd think I'm not 'doing grief right' if they knew it's not a day of significance to me at all, if that makes sense.
It would also bring my thoughts to the person's death, in quite an abrupt way, when in all likelyhood I'd not be thinking about it right then. I tend to think of people on their birthdays - and they're happy thoughts of past celebrations - or the usual day to day thoughts, but I don't want to specifically think about people's actual death.
I've also seen posts on here from people who don't like flowers in these situations because it reminds them of the bouquets they got at the time, or the funeral flowers.