I don't think you're legally required to do anything (like dropping a dime on her or anything). You have a picture and you're not sure what it is. You can drop it there (and I think you should).
With regards to whether you want the tenant out or not, if you didn't know about the bag of unknown plant material, what would you want to happen?
Now that you have a possible suspicion, does any of that change?
It sounds like you're inclined to end her tenancy, which is fine. If that's the path you want to take, do it as normal, don't mention the picture, and part ways as usual.