As djp said, the only time "mixed signals" come into play is when the two of you are having a private conversation that has nothing to do with school/etc. In other words, if you're talking about your latest homework assignment, that doesn't count (unless she puts her hand down your pants while asking you for help).
If you want to know what she thinks, ask her on a date. Worst case, she says no. Best case, you just found yourself a girlfriend. Go for it.
