What should I do about my daughter ?

I believe she knows who had the weed-smoke bags but doesn't want to tell, and I have a 15yr old who I don't allow to go to parties, because so much goes on, if I don't meet the parent my child isn't going I believe that she is telling u some o the truth no the whole truth, but I would ground her and take away all her possession ad make her stand-up until I tell her sit down no one wants to stand up their feet will hurt intensely.