I have a few questions about in the following sentence
To finish the report, Helen has stayed up late every night for the past week.
1. Is it OK to use "complete" instead of "finish"?
2. In the second part of the sentence, is it better to use present perfect progressive tense (has been staying up) or the present perfect tense(has stayed up)?
1. Yes. The extra connotation of "complete" is to fill in a form. So, if the report required simply filling in blanks or check marks, I would think "complete the report" would be more natural. But either works.
2. Either is acceptable.