If the dots are poorly connected, the reader can get used to the character and learn to recognize their touch, but you as the writer really shouldn't make your reader work for these connections. It robs them of some of the joy if they have to stop and wonder if the person in the second scene is maybe the same person as showed up in the first scene.
Remember, you're showing a blind person a movie he has never seen so you need to use your words to see for him.
Your clues can be as blatant as having this person be the one and only Gothic student in the school - an object of interest but not someone easily approachable, or you can use clues as small as a facial scar - something that doesn't disfigure but still attracts attention, while at the same time be hard to inquire after. By clues, I mean something you can mention, something you notice each time this character appears.
The girl passed me a note as she shoved on past. I noticed that she only had a gold hoop in one ear, and then I noticed why; her other ear had no earlobe, just a blue line where the scar cupped her lower ear and dripped down her neck. Did she have that tattooed? I couldn't tell before she was gone.Now the next time this girl appears, you might want to take a closer look at that ear but she's facing the wrong direction. And the next time you see her, you might take a moment to make sure you cross paths in such a manner so you can get that look.
The ear is the dots. You mentioning them is the connections. What she does is the important part of the story, be it pass a note or give some dark warning, or even something more up front.
Eventually this person might develop a name and maybe she will become a topic of conversation. She might even become a major character in your story, but if you go that far, the 'dot' part of her should remain one of those cryptic mysteries. I mean, what's the fun in revealing ALL her secrets.
The character I used in my trilogy wasn't even a character, in fact he scarcely qualified as a ghost, and he might have been one of two ghosts, it was sometimes hard to tell. The clues he left were indecipherable compulsions and confusing dreams and visions. He did his best to keep us all confused throughout the story. hahaha Did he keep you guessing too?
So what are the 'dots' in your story, and how have you connected them?