Do we ever find out who these people are that she seems to be seeing?
Here is the relevant book quote where Janet is telling a story about Emily Greenstreet:
"Maybe you knew this, I don't know, I didn't, but Woof used to be different from the from the other fountains. That's why the doomers started hanging out there in the first place. You wouldn't notice what was off about it, at first, but after a while you'd realize that when you looked into it, you wouldn't see your reflection, just empty sky. And maybe if the sky was cloudy on that particular day, the sky in the fountain would be blue, or the other way around. It definitely wasn't a normal reflection. And every once in a while you'd look into it and you'd see other faces looking up at you, looking puzzled, as if they were looking into some other fountain somewhere else and not their own. Somebody must have figured out a way to switch the reflection in two fountains, but who did it and why, and how, and why the Dean didn't change them back, I have no idea.
"You have to wonder, too, if it was more than just the reflections--if you could dive down into one pool and come up in the other one, in this world or some other world. Did you know they were here before Brakebills? They build the school to be near them, and not the other way around. Or that's what people say."
"Well that's what people say, darling. Anyway," Janet went on, "the thing is, Emily started spending a lot of time at Woof, just smoking and hanging out, and I guess mooning over her little affair. She spent so much time there that she started to recognize one of the faces in the fountain. Somebody like her, who was spending a lot of time at the other fountain, the one in the reflection. Let's call her Doris. After a while Emily and Doris got to noticing each other. They'd acknowledge each other, a little wave, you know, just to be polite. Porbably Doris was a little mopey, too. They got to feeling like kindred spirits.
"Emily and Doris worked out a way to communicate. Again, the exact details have eluded your intrepid correspondent. Maybe they held up signs or something. They must have had to be in mirror writing, to make sense as reflections, or am I getting that wrong?
"I don't know how things worked in Woofland, where Doris lived, maybe magic is different there. Or maybe Doris was fucking with our Emily, maybe she was sick of hearing Emily whine about her love life. Maybe there was something really wrong with Doris, maybe she was something genuinely evil. But one day Doris suggested that if Emily wanted her lover back, maybe her appearance was the problem, and she should try changing it?"