When she is there with you, and it comes up (it will), remind her that it is ok to be sad and that it can help to talk about how you feel. She can draw pictures for her friend, or write notes to her friend and put them on the grave if that is an option.
Give her time to talk, let her know you are there for her whenever she needs to or wants to talk.
There are a few books out for children about grief, not sure what for 10 year olds as my daughter was 6/7 when she started dealing with loss.

Biggest thing, it's all a process and nobody follows the same one. Some days maybe she'll be sad, other days, fine, other days angry.

My 10 year old still talks about the loss and the grief that she has gone through