Your dog is named FEMA?
note the lack of my usual 'take over a cake and offer to bury the hatchet and be friends' speech. It's probably fairly obvious why I didn't include that speech.
Build a 6' fence around your entire yard and see if she can lift her dog over that, then, buy a video camera to video her son smoking joints and throwing them on your yard, and send it to the cops.
Accompany it with a sweet letter:
'Dear Officers, I am concerned that my neighbor may complain about me and accuse me of drug use because she is angry at me for complaining to her about her dog poohing on my lawn. We have had other difficulties related to a duckling of mine tresspassing on her property. The duckling was a minor at the time and was panicked and swears it was not an intentional tresspass. This video shows her son throwing marijuana cigarettes on my lawn. I try to clean them up but he is doing it all the time. Thank you, Mrs. Frances R. McDiarmad' (or whatever your name is).