Denise,
When I shot my first two weddings, film, I shot with one camera and 20 rolls of film, 6x4.5, so that was only 300 shots. I had an old TLR(twin lens reflex) as my backup and two strobes on a flash bracket. Since your my age roughly, maybe a little younger, I bet you remember TLRs

. I shot weddings this way for a couple of years. Had to pick up my TLR one time because my winder broke on my Bronica. I had so many inquiries for weddings that I was turning them away, only did 6 a year at that time. My only advertisement was word of mouth. People told me thay wanted me because of my passion. I suspect that is why she wants you while knowing its your first time. She sees your passion in your work.
Take the wedding with what you have, just be up front with your customer, which sounds like you are. I think I would opt for the 7D rental mainly because I remember you had to send your 7D in once if
I remember right. Otherwise, if you know someone that will loan you a rebel or something. I hate Rebels now but my first digital wedding was on an 8mpix rebel. They can take pro quaility shots in the hands of someone like you
Keep it simple for the first one. Make sure you take your battery charger so half way through you can plug your camera batt in while you continue to shoot. Thats what I did with my first digital wedding.