her, she

'She' is used as a subject, while 'her' is used as an object in a sentence. When using 'she' or 'her' as one of two subjects or objects, an easy tip is to use the one that makes sense when the other subject is omitted.

Incorrect: Paul gave the assignment to Andrea and she.
Correct: Paul gave the assignment to Andrea and her. (Paul gave the assignment to her.)

Incorrect: Her and Steve worked on the same project.
Correct: She and Steve worked on the same project. (She worked on the project.)