This fits with your last theory. I'm doing this from memory so if anyone remembers jump in.
The nanny is the one that saw her in the water. Then she called Howard who called Big Moe. Your theory would still work in this scenario if like you said Howie turned a blind eye. From what was said she was dead and Moe was able to bring her back that time. I think Moe also said she wasa very grateful to him.
Larry said that Danny did not like the Bahamas so maybe it was the Gibsons. Still I'm thinking it was Howard and he was ramping up his controlling ways. I wonder if Larry told Daniel about the incident in the hospital while Anna was trying to detox.
When you say Howard called Moe, do you mean by phone, or was he physically at the home and yelled out to Moe?
Because if HKS was then here we go again with one person telling another person telling another person and nobody calls 911 while Anna is actually drowning and near death.
If Howard was home, why didn't he jump in the pool and save her himself?