study abroad (=travel?) while waiting for GC

My employer has filed my Labor Cert in Dec/02 in DOL Seattle for me and my family. Waiting time for it to be approved now is around 18 months. My daughter wants to go to college in Canada to study. Can she go now for at least those 18 months? At what point does she have to be back and not leave the country if at all? At the time of filing I-140? At the time of approval of I-140?
I appreciate your answer, her college application deadline is 1/15.

My employer has filed my Labor Cert in Dec/02 in DOL Seattle for me and my family. Waiting time for it to be approved now is around 18 months. My daughter wants to go to college in Canada to study. Can she go now for at least those 18 months? At what point does she have to be back and not leave the country if at all? At the time of filing I-140? At the time of approval of I-140?
I appreciate your answer, her college application deadline is 1/15.

You are the one the labor cert was filed for, so you are the one who has to stay here or lose it. When you're at the step when you apply for your green card, your daughter can get hers at the Canadian consulate as long as she's still under 21.