What could Brenda have done differently? Brenda is not a stupid person, and she is hardly to be blamed for not anticipating situations completely out of her experience with Brad or anyone else for that matter. But there are some things Brenda could have done to protect herself, family finances and property, and her peace of mind.
The first thing Brenda could have done when living with Brad became so strained that she was considering asking him to move out is call a domestic violence hotline for a confidential conversation with someone who could listen to her and give her some perspective on what might be happening, and what might happen next. This person could help her evaluate Brad's potential to be dangerous, something which might be hard for Brenda to face, but severe stressors and drug use raise the risk of something very bad happening.
Why a domestic violence hotline? (Brenda doesn't want to go into a DV shelter and she may be angry and frustrated with Brad, but she may not be afraid of him.) Because domestic violence personnel are uniquely equipped, unlike therapists, clergy, marriage counselors, family doctors, and even police, to have a calm, frank, nonjudgmental conversation about what's going on behind the closed doors that every family presents to the world.
Brenda could also have looked to the collective wisdom of the internet, which, though no one source is infallible, offers so many points of view that if you are looking to learn about your situation, bits and pieces can add up to quite an education in a short time. She might even have read an article like this one.
Resource Quick List:
National Domestic Violence Hotline - They care about your safety on the computer and give instructions up front about how to keep your visit to the hotline from being tracked.
Safety Planning - Same site as above. This is the direct link to safety planning resources.
Brenda could have gone to the library or bookstore and done some browsing in the marriage self-help/divorce strategies section. She could start reading a copy of "Why Does He Do That" by Lundy Bancroft. Chances are good she will find her story in its pages, along with an outstanding analysis and prediction of what lies ahead for her and the children. Scary? Maybe a bit. But at this point Brenda is already scared, and adding being completely in the dark about her situation isn't helping. Some expert advice and wisdom is just what she needs.
Any of the above could have alerted her to how vulnerable she was - Brad has moved out but they have not gone to court to get an order for temporary custody arrangements. Alerted her to the need to change her locks, secure her mail with a PO box, change the passwords on all the computers and online bank access, and not let Brad back into the home.