Eating grass

Brooklyn, my 8 mnth old pit eats grass, grass and more grass. My older pittie does eat grass ONLY on the occasion when she is thirsty and we are outside, so she resorts to grass. But Brooklyn is crazy for grass, this all she does when we go on long walks, eats TONS of grass. I tell her to stop, she does, then I turn around and she is eating more!!! She used to throw it up, but as shes getting older, she is now pooping it all out. I am beginning to think I shouldnt waste my breath anymore, yelling at her to stop......or is this bad for her, is it something I should worry about?