The Girl in Red...

Jolly Doll wrote:

You don't get an envelope from every encounter. From what I read on another site you don't get envelopes when Rin encounters her.

You actually do get envelopes with encounters from Rin. If you're not getting envelopes and are seeing her, that means you already got those envelopes in a previous playthrough. In order to get ALL the envelopes make sure to see all of her locations in one playthrough. If you miss one, you'll need to play through the game and not only see the location you missed but also see all her locations again even though you already saw them in the previous playthrough.