For calling / messaging, it’s dependant on how close you are and whether you would normally call or message. But a message is a fairly safe bet that leaves her the chance to respond in her time. (Assume that you won’t get a reply)
If you are (proximity wise) close by then an open offer to do anything is nice.
Flowers are a personal matter, they could be appreciated as a thought, but they could also be inundated from others.
Just to know that those who care are thinking of you and are available if needed, without the pressure of a response needed can be valuable.
When I lost my best friend I was zombified in auto pilot. I did have things to do from day one, looking after their birds and contacting particular people whilst being unable to ‘actively’ function (I blocked out much of the world!) and then gradually switching myself back on occupied with tasks to do.
You will be feeling your own grief, there is no right or wrong way to grieve. Just allow everyone to grieve their way and be available to those who may need you
You may need to block out others and keep things to yourself, but don’t let that go too far.
If you don’t feel like talking with those who are around or it is too difficult to do so, then use strangers and / or distant friends.