Could it be that the responsibility Bree talked about after her ceremony has to do with subjugating this evil god? Bree's purity was a major issue at one point probably because she needs purity to effect the evil. Dealing with an evil god is certainly dangerous for Bree but I don't think thats why Daniel is in danger.
Lets say you are a part of an ancient order, hundred of years old, burdened with the awesome responsibility of preventing the return of a great evil (sounds like a video game to me

Lucy is one of them and her job was to keep Bree focused. This includes keeping tabs on Daniel. Thats why she has pics of Daniel and I bet if he looked further he would have found pics of Cassie too.
For whatever reason this sort of thing needs to be kept secret. When Daniel broke in it was absolutely neccisary to take action against him. They probably were hesitant to take action because anything they do would bring attention to themselves but at that point they had to do something.
Only Bree can save Daniel. Soon she will be breaking into Lucy's apartment.
Well I talked alot and probably butcher the heck out the plot. I don't care if you flame away just make it amusing.