I am very sorry for your child's troubles.
I am not a lawyer, not do I play one on tv.
However, if my child told me they were going to kill themselves, I would be concerned. I think you should try to find someone who's a pro she can talk to. It's well over my head I know enought to know that.
It's been alot of years since I was in 8th grade, but back when I was there, this does not sound like the end of the entire world. Kids got caught with pot and cigarettes all the time. Maybe she gets suspended or something?
Police officer threatening her with harm from dogs? I don't understand. I ran track and cross country. They used to have the drug dogs come into the locker room now and again, is that what this threat is? Yes, they used to do that, and they probably still do. They can go through your locker as far as I know.
I have a feeling your child is not telling you everything. The story doesn't even make sense. Why would another child hand your child a bag of weed and run away? Your child got scared and stuck it in her bra? Why not just drop it right there and walk?
I think if you look this situation over, based on your own post, it doesn't seem to add up.
If I were you, I'd be taking her to someone she can talk to about whatever her issues are.
I doubt they'll keep her out of school forever. Just get her head straight and I think it will be ok.
Good luck!