Well, it seems to me like most of the case sounds to be solved with just the lack of evidence, but anyhow I will put my import in…
Considering Corina’s history with substance abuse, it’s possible that either she was still involved in the business AFTER rehab or she owed someone money or something BEFORE rehab. But considering how it was said that she was seen in a drug house, it’s possible that she was doing unfinished business, like trying to explain herself to the people she owed but after the culprits (yes, by the sounds of it there was multiple), they decided to kidnap and torture her before deciding to kill her. Now, this is just my input from what I’ve heard. But it definitely sounds like she was somehow still involved with the drug business.