To use a pen name or not to use a pen name: that is the question.

(I know that was cheesy but bear with me, and as cliched as quoting it has become, I love that play.)

I have the opportunity to write a small piece to be published in a book that is compiled of such small pieces. The subject matter is extremely personal, and the powers that be have told me that it is okay to use a pen name for anonymity. This is what I would like to do, but I am wondering about how I will use it in my portfolio in the future. Obviously I couldn't advertise it on my website with my other work. But this will be my first publication in an actual book, so I am really torn. I am leaning more towards using the pen name, just because what I write will be so personal. Anyone have any thoughts on this?