What's the difference between 她很普通 and 她很一般？

大家好

I can't recall what the exact difference is between 她很普通 and 她很一般.  I remember having this discussion with a teacher before, but I cannot remember the outcome clearly.  It seems to me that she said  她很普通 is a bit negative, as if to say, "She is just ordinary," i.e. emphasizing she is not special in any way.  On the other hand, 她很一般 is more like saying, "She is average," i.e. emphasizing while not spectacular, she is definitely not a bad student.  I also seem to remember being told that 她很一般 can sometimes mean "very good," i.e. it is a modest way to praise someone, but again, I can't remember clearly.  

So are any of my ideas correct?

BONUS: Does the following sentence make sense?

他的钢琴弹得很一般，在我们班数得着。

Actually, this post was inspired by this sentence.  I found it in my old notes.  It seems to say, "She is very average at playing piano.  In our class she is one of the best."  This totally makes no sense in English.