It's in the closet on the last page. That slip of paper sticking out of Youko File 37 says 事故死を followed by what appears to be 装 (the character is partially cut off, but that fits what's there). That's basically "make the death(s) look like an accident".
hmmmm....what if we're all jumping to conclusions and she just collected those pictures to make a scrapbook to give as a gift to the maid to commemorate their friendship lol