The reincarnations are all introduced very quickly, and while I did get an idea of who Hugo, Schlain, Oka, and Katia were in their past lives (albeit after some initial confusion for Katia, since in the English dub, Shun's other friend, the one who wasn't Katia, had a voice similar to Katia), Yuri Ullen's identity and past role didn't really get across, to the point where I didn't even know what her name was (I now know it was Yuika Hasebe). The only characters of note were the two who accompanied Fei in her bullying of Hiiro. Was either of them Yuika Hasebe?
In short, no, neither of Fei's friends were Yuika. Just going by wikipedia, Fei's friends were named Aiko Iijima and Kumiko Tonooka. Yuika Hasebe does appear in the flashback episode, though she doesn't do much to stand out. Here's what she looks like:
She looks a bit similar to Fei, but could not be mistaken for either of Fei's two friends:
In the anime, the reincarnations are introduced very quickly (unless I'm mistaken, all five of the characters I mentioned were introduced in the first episode, without much context, and it's up to the viewer to figure out they're reincarnations), and I feel this was done poorly and probably led to my confusion. The light novels have less of a problem with this, as the reincarnations are introduced more slowly, usually one-by-one, and their past lives are explained at least a bit.
Yuri's introduction in the light novels actually rules her out as an associate of Fei. From volume 2, Chapter S1: Academy:
The girl scolding Natsume was formerly Yuika Hasebe, who used to sit next to me.
Unlike Natsume, Hasebe never made an impression of being particularly good or bad.
Among the girls, the clique that stood out most was the one that included Fei, aka Mirei Shinohara. But Hasebe was closer with the relatively quiet girls, like Temarikawa and Furuta.
Of course, that's just compared with Fei--she was still a pretty bright and active person herself--but Hasebe certainly never struck me as the type who secretly held the potential to be a saint or anything like that.
Back in volume 1, in the first Shun chapter, which actually takes place before everyone dies and is reincarnated, Hasebe is again described as "the girl with the desk next to mine". It seems she was intended to be a low-key character, one who even Shun doesn't take much notice of, whose basic identity to Shun is just the girl who sat next to him. I don't know anything about the original publication order of the chapters, but for the English light novels published by Yen Press, this is when Yuika Hasebe is first introduced, in the first volume, Chapter S1: The End of Normal Life:
"What's wrong?" Yuika Hasebe, the girl with the desk next to mine, responded to my grumbling.
"I forgot my pencil case"
"Oh, did you? Well, I suppose you can borrow these, then." Hasebe handed me a pencil and eraser.
"Mm-hmm. You owe me a piece of candy."
"C'mon, you're charging me?" I groaned, but I smiled wryly and waved a hand in acknowledgement nonetheless.
It's a pretty normal conversation, but helps characterize Yuika Hasebe a little bit... as someone pretty normal. She's perhaps a little quiet, and definitely not a bully.