L.C.
Send a card now.
Send a card in a few months.
Send a card a year from now... that's when most people forget and the pain of loss is excruciating...
The pain is real and it isn't going away.
This happened to a friend of mine - there were 3 of us who were pregnant at the same time. 2 had successful deliveries, the 3rd did not. We went to the funeral. It was awful!
She had a plate made with the baby's name (Thomas) and birthdate on it that hung in her kitchen next to the plate of her living child. Thomas will always be remembered.
There is nothing you can say that will make the grieving process any easier, but you can let her know that you remember and that you are thinking about her... that's probably the best gift you can give.
LBC