Ok, you might not like my advice, but I've had this situation come up and I nipped it in bud so it couldn't happen again. EACH of my clients now has my contract which also contains a non-disclosure, which states they will NOT discuss fees with
ANYONE. Before that I had same exact situation and your instincts are probably right like mine were, this client I got rid of before I even started, and we just nullified the contract. It wasn't just over that issue, it was more over the fact that I knew this was going to be a problem client from the beginning. I even did NOT discount their setup fee like I normally do because I really thought they wouldn't sign. Anyway, when that issue came up about the pricing, I politely told the new client that I do not discuss my billing arrangements with other clients. NOTE the period at the end of that sentence.. PERIOD.
I tell you this because it will probably be first nature to you to cut the provider some slack, lower fee, etc and that's a bad idea as it sends a bad first impression to that client.. they will figure if they can negotiate that..they can negotiate other things, and before you know it your pulling your hair out and bending over backwards.
So my response to her would be this, "We do not discuss billing arrangements we have with other clients" Our fees are based on each individual practice and their needs
. Also I would get out your contract and also add a non-disclosure clause