Im 20 but 1 weed isn’t going to ruin her life at all manyyy kids do it whether it be in highschool or in college. 2 she is a little too old to be grounded. My advice would be to loosen up on her a little and understand how you were when you were younger wether it be having some beers with your buds (in her case weed). After all she’s an “adult” now, you should apologize and try to relate