First, I would be sure to tell her what goes on during a viewing and a funeral..... tell her (if you/her choose to go to the viewing) that she can look at grandma's body, but to remember, that it is just her body, and not her. I don't know how religious you are, but there might be ways to explain how her spirit, the part that REALLY made her what we knew and loved was no longer there.
Tell her that there may be some people that are crying, and it is ok to be sad and cry.... that other people miss her, also.
Be sure to tell her that some people may tell fun stories and memories about her, and that is how she would like to be remembered, by the good and fun things she did for people.
Explain what might go on at the service.... some singing, some prayers, and sometimes people tell things about her.
Maybe give her the option of going? Also.... if she goes, and wants to leave, be sure to tell her that is an option.
Will there be childcare at the funeral? If so, let her know that she can go to the childcare if she wants, even during the service.
Ultimately, though, you are the one that knows her best... follow her lead. When my father died in 1991, my kids were 9, 7 1/2, 5, and 6 weeks. We explained what would go on, and gave the kids the choice of going to the service. The 7 1/2 yr old didn't want to go to the service itself, and stayed in the childcare with the infant. My 9 and 5 yr old did go. The service was held at their church, and childcare was provided for anyone that wanted it.