IS this correct?

Hello,
I am wondering if some of these sentences are correct, please tell me if they are or aren't and why:

1.She had her flowers watered while she was OR she had arranged for someone to water her flowers while she was away.

2.I said I will have passed all my exams by the end of the month OR I said I would have passed all my exams by the end of the month.

3. We all wish it wouldn't have happened but whats done cannot be undone OR we all wish it hadnt happened but whats done cannot be undone

4.this one is just about whether it is to hide behind a bush or in a bush. (I think both are acceptable)