I do think it's possible she has a personal relationship with him beyond just being the mail carrier for his house/street. I'm not saying I think they're close friends or anything like that, although who knows - they could be. I think one or both of them probably would've mentioned that though. I just think they know each other better than, say, I know my own mail carrier.
I didn't mean to imply that she has a reason to be biased about the case. Thanks for asking so I could clarify.
I believe she's pretty sure she saw Dylan and that she would recognize him. I wish we knew more in terms of why, because it seems strange to me that she'd be able to recognize him, potentially from a distance, if she doesn't see him often. It would make a lot more sense IMO if she knows MR/Dylan outside of just her job, or if she knew Dylan before (i.e. if she has a child who went to school with Dylan). I don't feel like she's being dishonest about what she saw or thinks she saw, though.
I feel for her. If she is completely sure she saw Dylan, then at this point she's the last known person to see him, other than the boy he was walking with. She's also the only person other than MR who can back up MR's story that Dylan was alive that afternoon. Seems like a lot of pressure on her to be sure that she's right and could definitively recognize Dyaln, IMO. If that makes any sense.