She could easily have been packing a small quantity of hash, which if ingested would cause her to test positive for marijuana.
Occam's razor. What is the simplest explanation?
1. A guard permitted her to chain smoke a large quantity of marijuana in her jail cell.
2. She was able to smuggle in a small quantity of hash (hollowed out tampons are often used for this purpose), which she ingested in jail.
3. She ingested a large amount of marijuana or a small amount of hash in her car during the 10 minutes or so that she was alone while the officer was checking her driving license.
I don’t know about ‘simplest’, but #3 fits the facts and the video.
I’m not sure that even if she did consume some form of THC that it is what caused her to hang herself. Sounds like she had ‘suicidal tendencies’ and it was just a matter of time before she was successful.