Hey! Thank you for playing!
She doesn't actually say when exactly, because she refuses to talk about the actual location of the murder. You will have to slowly eliminate all the options until there is only one left.
If you are still stuck here's a tip: They were still together at Cozy Camping, but she was alone on the viewing platform.
Also, the last node you need to find for a perfect game is quite hidden. You need to really look for a way to that dialog point! But you can also just take a guess haha :D