I'm sorry for the loss of your Grandma.
I was raised that you go to all funerals and weddings, so by the time I was a adult, I've been to many funerals. I was never traumatized by them. My husband was raised that he didn't go to funerals, and feels a little resentment that he wasn't given the choice to go to his Grandfather's funeral, so he didn't say his goodbye's.
My belief is that death is a natural part of life so I have taken my kid's to our family funeral's. It gives them the chance to say their goodbyes, and also see people being honored and remembered for their life.
I think in the case of your 5 year old. It is her Great Grandmother, so if you feel comfortable with it then she should go. If your husband feels uncomfortable about the viewing, then either go up first and make sure that your Grandmother does look peaceful, and then prep her and go up with her while she views her. Or, missing the viewing is not the end of the world so she doesn't have to go up there.
In anycase, whatever decision you make, will be the right one. Once again, I'm sorry for your loss.