I would tend to believe this simply because it is so weird. People make up lies that they think others will believe.
Notice, she makes no claim the husband was threatening her. She didn’t delay calling the police. Was apparently distraught. She even admitted to doing it. If I were on a jury I’d believe her.
She made a good argument for buying both a pizza wheel and double-sided rug tape.
She may have also made a good argument for owning a cat instead of a dog.
What I would believe as a juror, since as you say it is weird... is that this happened in the recent pass just as she described but that at the last second she was able to point the knife away as a natural reflex.
Later, after giving it much thought she realized she could have killed her husband and then basically recreated the scene enough to kill him.
Especially given their history of police being called seven times because of loud arguments.