The loli didn't just write insults in big letters on Rika's notes. There were also several parts where she had crossed out. That implies that she was pointing out the parts Rika had wrong in her notes. So there are only two possible explanations for how a grade schooler is able to correct the mistakes of a high schooler. She is a genius. But that only makes sense if she's in advanced classes, or skipping grades altogether. Or, the loli remembers her past life. That would explain her intelligence. Both possibilities would explain her smug attitude. The advantage of the past life storyline, is that it creates moral justification for Rika to date an 8 year old. "She's only physically 8, but has all the memories of her past life." Still illegal though...
I'm liking the plot and characters so far. The fact that Rika is trying to fight against being a lolicon and the loli knows what she is, and is already tormenting her, makes for a very interesting dynamic.