Dismissed vs Not Guilty

[dqer]

My question involves traffic court in the State of: California

My friend went into an arrangement for a citation minor in possession. The judge offered the option to taking a traffic class and stated that the charges would be dismissed after the completion of the course. I was with her during the incident and she was not guilty but she decided to take the traffic class that the judge offered.
1. Would it make a difference whether or not she pleaded 'not guilty' and having it 'dismissed' after completion of the course?
2. Will the 'dismissed' charges appear on her records?
3. After the arrangement she received a paper with a "PN" written under her 'PLEA' What does this mean?
4. What are the difference between a case that was 'dismissed' and found 'not guilty'?
Thanks!!

[M'sta Mikey]

A plea of not guilty would have resulted in a trial in which she could have been found guilty.

Dismissed means just that; she completes traffic school and the charge is "wiped" from her record, as if it never existed.