K.B.
As the below mom suggested; a card with an added personal note saying something like 'If you ever need to talk I will listen, if you need a hug my arms are open, if you just need someone to sit with and to hold your hand my door is open.' That way she knows you are not going to try and say something to make her feel better BUT you will be there for her.
If you want to get her a small gift maybe a bracelet or necklace (religious cross, angel or have it in a favorite color of hers... whatever her style is) to be a remembrance of her angel, it does not need any special charms unless she likes that type of thing.