I charge by the number of servings. In my area for fondant it is 4.00 per serving. The gum paste flowers are extra.
What sizes does she want? I have never done a wedding cake, but I do sugar flowers. They are super time consuming. It would depend to on what kind of cake she want. I would probably charge at least $3.50/slice but I am not experienced in selling.
A bride brought me that exact picture yesterday. 100 servings, 3 side clusters of flowers (instead of 2 in the pic), fondant ribbon (I wont use satin ribbon) 100 servings, flowers, including equipment and delivery, $505