Hi Olena. That's a good question
If that phrase is a question, then it should have a question mark. The answer could be "because i'm running late and I don't have enough time to help her"
If it's a suggestion/order , it doesnt necessarily has to have a question mark, it's a matter of how nice do you wanna sound when you give said order or suggestion. In that case the other person won't answer with an explanation, they will go and help the lady or the will refuse.
That's my point of view, cheers!