I think it's safe to assume that it is a fan created mod for the PC version of SH3. That or they updated her alt costumes for the HD version.
Yeah I thought it might be a mod also, I've been checking around for it on Google, but I can't find anything on it, oh well. Also it isn't in the HD collection either, I have it, and a lot of the costumes are missing they certainly didn't put in any new ones. --- "Greater love hath no man than this, that a man lay down his life for his friends. John 15:13"
Yup, that's a PC mod, i have all the extra outfit passwords written down and that outfit is definitely not one of them. --- I am a dedicated member of the "Walter Sullivan Is Bad-Ass" group!!! I am the true originator of the Cookie Demon theory on the SH2 and 3 boards.