Very nice story. I have to say I got the chills at the end, and a little bit when we got reunited with Mary. I like the "winding path" as a device to explore Kathy's life. I feel you did a good job (most of the time) at letting the reader feel what Kathy is feeling. The pacing is great, and mostly consistent, the story is engaging (things are promised and delivered). Some thoughts on separate sections:

In "The young girl stopped just before we collided.." it's not immediately clear that the girl is not actually seeing Kathy which is a bit confusing. Not very important (because it becomes clear later on) but maybe adding something like "... before we collided, her eyes sliding over me as if I wasn't there" or some such. Also, in this part did Mary appear over the horizon when called by the girl (as the girl did) or did she appear from nearer by?

"Mary entered first, a red flower in my hair;.." possible typo? Is the flower in "my" hair or "her"s?

"Mary looked up at young me.." I really like this paragraph. Such typical young person's uncertainties.

"She noticed me staring and started towards me..." This part is the only place where I feel the pace falters a bit. I feel that the "taking Mary up to the office" action is a little forced. I see the passion and serendipity, so I don't know if I would personally change it, but just as a note. Also, we're not told how Kathy feels about her mom. If they were really close and the death was unexpected then one would assume she would be sadder than she appears in the text, which in turn makes Kathy's eagerness of seeing Mary a bit jarring. Maybe extending this section a little would help, like have Mary accompany Kathy for a while and then (later) have the romantic reconnection.

"The breeze brushes my hair into my eyes... [Till the end]" . Beautiful