I just don't think she would be hangin with him as much as she did if she thought Howard killed Daniel or if she felt that she was in danger. It doesn't make any sense at all.
I can think of a scenario, where accidently Daniel drank ANS methadone drink and she felt responsible and knew that Howard knew what happened. He could have also planeed that to happen and make her feel like she was the guilty party by switching drinks.
He then had even more control and said if we get married we don't have to testify against each other or something along that line.
I disagree - at this point he my have hand her under his thumb enough to control her. Kinda like how a abused woman stays with her abuser.
I just read back and found your post -- this is good Mom4K. I think that is very likely. HKS may have orchestrated it "accidentally on purpose" and made Anna think she was ultimately responsible. She may not have believed he would/could do it intentionally (which he may have), but in the end she felt it was HER drug addiction that caused his death. She certainly seemed to spiral downward after that.
The grief mixed with guilt must have been unbearable. And HKS used it to wield even more control over her, the finances etc...
The worry for HKS had to be what ANS would say at the upcoming inquest when pressured under questioning. I am sure HKS preferred that she not testify at all. And, maybe it was too much for her as well.