IMO, it's highly unlikely Maricela was a CI. Research prop 47, nobody does actual time for drugs anymore since its passing. It's also not at all unusual for them to initially charge someone with selling and later drop it to possession.
I also don't think having a BMW indicates she had a lot of income. What year is it? If she has a 15 year-old BMW that's not going to have much value. Now if it's a 2016 or something, that would be worth noting.
I think the sleeping in her sister's room and sudden feeling like she was being followed was either due to a mental health issue or drug use. Since the police said she's gone missing before, I think maybe she has gone voluntarily. Or perhaps she ran off trying to avoid whomever she thought was chasing her, and in doing so encountered someone who took advantage of finding her alone.
I really hope she left voluntarily, at least then she's probably somewhat safe.