I'm playing a combined hood (Pleasantview, Riverside, Desiderata Valley, Bluewater Village and Downdown) and I'm at the part where I've sent all the premade teens to college (they are a lot). I split them between dorms in SSU and Academie Le Tour. I had almost finished playing their freshman year when I realized that I had... forgotten Melody Tinker, so I placed her in a rental house byherself, played her until the beginning of her sophomore year and then I moved her in the largest dorm in SSU where I had only 5 more active sims. Her performance bar was fine while she lived on her own and she had, if fact, done her term paper for the new semester but after the move, her performance bar looks like you can see in the screenshot and it doesn't move "higher" even though she has the required skills and she has done her term paper (there is no option to do it again in any computer) and she attends classes every day.
I tried resetting her and getting out and back in of the game but it didn't fix her and now I'm afraid that she is going to fail this semester. Is there anything I can do to fix the situation?

If the glitch is graphical she won't fail, because its only a graphical error and not her actual grade showing.
Try moving her out and back in or look at options on the Pizza box by Cyjon http://cyjon.net/node/148

joandsarah77, thank you so much for helping me. I got Cyjon's debugger (I have so many of cyjon's hacks but I had no idea about this one and I'll have to confess that you calling it a "Pizza box" baffled me a bit, lol!) and it proved what you suspected, that it's only a graphical error. The end of the semester proved it even further because Melody is again on Dean's list, so she is fine. The weird thing is that, even though, the semester changed the glitch wasn't fixed so, I guess, that it will stay until she graduates and I'll have to make her do like a ton of assignements just to be safe, since I can't see her perfomance bar. But thank you again!

I often get this glitch and there's no need to go to extra effort to ensure her grade is acceptable. The glitch is almost invariably attached to a lot rather than to a sim. If you take her to a community lot and look at her grade bar, it will appear normal. If it gets to be too annoying, you can usually cure it entirely by moving her into a different residence. But you don't really even need to do that. Make sure she has enough skills to open the gradebar up, then let her go to class at least once and do one term paper. She'll pass, and she'll probably dean's list, because she'll spontaneously do research and assignments when you're playing someone else.