I apologize if this question is not allowed, but I'm worried that I over quoted for this cake. I felt confident with my quote at first, since I'd originally based my quote on 12 servings, but in getting feedback from other bakers they say it's more accurate to get 8 servings out of a 6 inch cake. 

I am covering this cake in all fondant, with the 2 flowers, the silver fondant clippers and comb, and a custom acrylic topper similar to this one but with the birthday girl's name incorporated into the acrylic design. (I'm spending $25 alone for the topper from an Etsy shoppe). I'm also dropping it off at the restaurant where they're hosting the party. It's an intimate dinner for up to 8, which is why I suggested she purchase a 6 inch cake. 

How much would you charge for this cake? How much would you charge if it had real roses or dahlia's instead of gumpaste?  Thank you in advance!

If you had taken any time at all to search other pricing ?s you will find that there is sooooo very much that goes into pricing that it is hard to give you a suggestion.   How much (complete total) did you spend on all ingredients, packaging, time shopping (gas etc), cost of electricty to bake, decorate etc?  What is the going rate of similar decorating in your area?   Are you in located in a rural, small village, town, city, or BIG city?     I'm with you that a 6" 2 layer cake will serve 12 to 15.  The difference in price between real and gp is $0.  In fact gp probably is a bit more expensive due to the time and talent it takes to make them.