Oh, Victoria, I am so sorry for your loss. And I can relate as my Dad is in the hospital dying, and we (family) have been discussing this very thing.
I DO plan to fly by the seat of my pants and remember him the way he was, not as he is now with kidney failure and dementia, and concentrate on the fun times we had while I was growing up, the way he has been with his grandchildren, and hopefully share some laughter along with some tears.
Write your feelings down on paper and read them at the service. They can be in the form of a poem, a story, or short descriptions of your friend and how she lived her life, the things she taught you, and why she will forever be in your heart. Consider making a copy for the family to keep as the service may be a blur for them, and they will have something to look back on.
God bless<3