Here's my perspective from what life and experience has let me observe on this topic. I'm going to state only what I have observed in real life experiences.
1. NOT ALL women talk about penis size with their close friend or within a group setting with other women. Some just simply don't talk about it.
2. SOME women do talk about penis size with a close friend or within a group setting with other women. There are always going to be some women who talk about it.
3. SOME women who do talk about it do not, under any circumstances, want men to know they talk about it and tell men who ask if they talk about it that they don't when the reality is that they do. In other words, some women are dishonest with men about whether or not they talk about it BUT just because a woman says she doesn't talk about it doesn't mean THAT women is lying. She maybe one of the ones who doesn't talk about it an is telling you the truth.
4. I know of a few women who have talked about it with their female companions because they were looking for a man with a big one for casual sex. Is that really that big of a surprise? And you can pretty much rest assured that women engaged in that kind of effort don't want other people (especially men) to know about it.
So, what we can take from this is that some (not all) women talk about it. Some women talk about it and then genuflect to men and say they don't.
You will probably never really know whose being honest and whose not because people can tell the truth and they can lie too. It's not worth worrying about.