Ask her if she feels like there is a dark cloud over her that just won't go away. It might be an easier way for her to realize that sometimes it takes talking to a professional to make the "cloud" go away. Reassure her that there is nothing wrong with her and that it's only because she experienced something really sad. Tell her that you can find a "stranger" for her to talk to because it would probably be easier if she doesn't think she would be comfortable with anyone at school.
Have your daughter make an album or scrapbook about her grandma. Sometimes we just need a way to mourn if we don't know how. Help her find pictures she can go through. She can add poems, draw pictures, make collages, add recipes, etc. Have her think of other things to add that remind her of her grandma.
Getting her involved in activities at school, in the community, at church, etc. is also a good idea from a poster. Ask her what she thinks her grandma would have liked to see her do. Remind her how proud her grandma would be if she did ____ or ____.