If you don’t want her to second shoot and the organizers are concerned then suit up and tell her that you’re moving in another direction with a different photographer. Being passive aggressive is for the weak. You’re being commissioned to do a job. It doesn’t matter how much the pay is. The expectation is you will produce the best results. If the second shooter doesn’t leave you with a warm and fuzzy feeling then let her go. Simple as that.
My other $.02 is don’t take on projects that are out of your league. Learn the relationship between flash and ambient light. It’ll save your butt one day.