I am a breast cancer survivor. I was diagnosed in December '09 and had a double mastectomy this January. I am going through chemo now. Having said all of that, it doesn't bother me one bit to see a woman nursing her child. This could be due to the fact that I was diagnosed after I had my two kids (and nursed them both) and wasn't planning on having anymore children, so I guess I feel like I didn't really "need" them anymore. I don't know if I would feel differently if the situation were different (i.e. I didn't have any children and wanted to in the future). I do get a little bit nostalgic when I hear of a friend who is pregnant or has a newborn (especially with #3 or #4) because I think "am I sure I was really done with kids?", but the bottom line is that I won't be having anymore and my diagnosis makes me appreciate the ones I have even more. They are 2 and 4 years old, so if this was found any sooner, I may not have my son and if it was found much later, I may be dealing with a cancer that wasn't curable (it was very aggressive).
I'm not sure how she really felt about it....only she knows that, but I would not feel bad if I were you. She didn't seem to make an issue of it since she told you that anywhere was fine. I'm not sure I would mention it because she has probably moved on from it if it even bothered her to begin with. If you feel like you have to get it off of your chest (so to speak), then I would just tell her (without gushing and making this conversation super emotional) that you apologize if nursing your infant in her presence made her uncomfortable or if it was painful for her in any way. Then, leave it at that. It has been my experience (in the 6 months since my diagnosis) that other people are much more hypersensitive to things related to my cancer than I am. I have had a lot of friends talk about hair care, hair products, etc. since my chemo (I have no hair now) and then they realize it and feel awful. I just laugh about it because I know that it will eventually grow back. I even had a very close friend offer to give me some shampoo that she forgot to pack and didn't want to bother with when she was moving. She was mortified as soon as she said it....I thought it was hillarious. Again, I'm not sure where your friend is/was mentally with respect to her cancer, but I am a Christian and I believe that there is a purpose to all of this that I just don't know yet. I am confident that I am going to beat this (my prognosis is excellent) and while I may not have my breasts anymore, I have the rest of my life with my kids and you know what? They can do AMAZING things with plastic surgery these days, so I'll look better than ever! It's all in how you look at it. :-)
Sorry this became so drawn out. I just wanted you to know that while you may feel horrible about all of this....if it had happened in my presence, I would have been perfectly fine with it. I truly think people are more upset and on edge about what is said in my presence than I am. I hope this is helpful in some way. I feel like it became a bit rambled...sorry for that!