Except in this case, the "bickering" appears to be the type related to DV: control of a person (SM) through money, appearance (what she could wear) & threatened gun violence (BM gun to his head.
The evidence we have does not indicate their known arguments as normal "like many couples." Once more, IMO. Perhaps you don't agree it is "evidence."
No doubt, once SM decided she wanted more autonomy as a person (thoughts, choices, actions), her husband saw it as a sign of opposition.
Bickering is arguing about petty or trivial matters. When Suzanne acted outside of the norms Barry was comfortable with, emotional coercion moved to physical coercion.
You can lose your life to DV, as we have seen in this case. Proving it is the challenge, especially when an interpersonal dynamic has consumed most of the party's adult lives.
JMHO