The only theory I don't go for is the...
toothache theory. Okay her tooth may have hurt but she was such a perfectionist that she decided to not just stop? Wouldn't the perfectionist theory also mean that she would not want to leave the legacy of a horrible mistake with people hating her for life. She could have just as easily called her husband and with him being so whipped he would have kept his mouth shut about anything.
The murder-suicide theory and the closeted alcoholic theory make more sense to me.
I am more for the closeted alcoholic theory. She kept it a secret and her husband may have possibly known she was a functioning alcoholic. Either way the husband and the sister in law are in denial about her. You want to shake them and tell them that, "Sorry she was drunk and high. Science doesn't lie. The police and no one has any ulterior motives to lie about her." Even if she did have a tooth ache she still chose to drink and smoke pot. That still puts her at fault because she knowingly drove after drinking and she did so with minors in the car.
Sorry if I come across as heartless but I just have no sympathy for her. If she survived that crash she definitely would have been charged with homicide and she would have been in jail for a long time or possibly life.