That sounds lovely What a special friend you are. I have heard that some mums dislike flowers, when a friend of mine lost her twins last year I bought her a simple silver chain and two little silver and CZ-studded star pendants to put on it, and popped it in a card with a little note to tell her how sorry I was and that I was thinking of her. Maybe if your friend wears a bracelet (eg a Pandora one, although most regular link bracelets work these days) you could buy her some charms or something commemorating her little angels?
HTH, I think your friend would be very glad to know that she has someone there who cares and is willing to listen. *hugs*