Copy off some important facts... like how many children in the US and outside the world are circ'ed. Along with well anything you wish to share... If she askes, have the envelope ready and respond with... Oh, you know your bringing it up before really made me look into it, and this is what I found out, but I didn't really know how to bring it up. Hand her the envelope, and then I would reply with as for now I don't see a need to alter what is already perfect, I hope you take the time to look through what I have given you, but I just don't feel good about it, that and the more we have discussed it, we have decided that its not our choice to make, its his.
This could open the door for her saying wow... I had no idea, and if it doesn't well I suppose at that point the answer would be, I really don't want to discuss this anymore.
If she gives you hassle and comes up with doc. that are pro circ... well you know where to come to copy off anything to counter it....
Help her see a bigger picture, if she can't well tell her you love her so much that you didn't want to shut her down, but just wanted to share why you feel the way you feel, but your minds are made up, and you would feel better if it wasn't discussed anymore.