I am not too sure if I understand, but I take it that it means that she has started school 1000 days ago.
So we have to calculate the number of working days in the last 1000 days: we know that in every 7 days, 5 days are working days. (let's ignore the holidays for now... for this we need a more detailed information about when it was).
So to calculate this, we calculate: [tex] \frac{5}{100} * 1000 = 714.285.
[/tex]
so an actual number of days could be 714 or 715. If we round it, it's 710 (or 720 if it was 715 indeed)...