All speculation & moo....certainly not meant to defame the victim MB but we're all adults here & we know that "happily ever after" isn't always reality. It's painfully obvious to me that BB & MB didn't have a happy marriage--we have all noted such ad nauseum. That being said & without judgement, here goes:
Hubby BB or anyone in his family didn't do it.
It is my personal theory that a female, rage-fueled, lied to spouse found out about something that went on in Austin. Her suspicions were true. She knows her hubby has eyes for a very attractive CG instructor MB & it seems like they have so much in common. Like they were made for each other. She believes this. She must get rid of her or her life will fall apart & she can't have that. She may have confirmation of this through notes, texts, phone calls, stalking them, evidence left on his clothing, etc & maybe all of the above. Somewhere it is indicated (maybe in BB's FB) or other communications that this pretty CG instructors hubby will be out of town for a few days of fishing. This jealous female spouse knows this is her hubby's & MB's secret time to get together--Her CG Instructor hubby & MB. Fireworks! I must say that if there was an affair going on, it could be real or it could be a delusion inside the mind of this jealous wife.
Now jealous wife finds out that some reandevous has been planned between her hubby and our victim while the hubby is away on a fishing trip (or she assumes in her mind & heart it will occur). She's not going to let that happen. She kills her "competition" before there's opportunity for any night where they could be together. She kills to nip it in the bud 'cause hubby can't seem to do it.....and she feels maybe MB can't either.
I feel this jealous female had given MB warnings to stay away from her man-maybe secretively, maybe subtly, maybe ominously like "leave him alone" notes left on her car because jealous female wife wasn't 100% sure but she suspected. These "warnings" scared MB as they should have & that's why she was acting a bit reserved according to a gym buddy. MB was concerned but she didn't know how serious she needed to take these threats? MB may have felt she was being "tailed" or stalked but she wasn't sure. MB told no one & hoped it was all just some whacky prank.
Yep, jealous female spouse at the brink of insanity did it.
Of course, divorce was the sane answer but she is obsessively in love with her husband & for a variety of reasons (hormonal swing & not taking meds) isn't thinking straight. I think those that know her understand she is a French fry short of a happy meal. She wants to be so much more attractive than what she is right now...she used to be when he fell in love with her. In her world, it's all about him. She is sick. The whole CG thing has ruined her life, she feels. She felt like she was playing a game against MB but she took it too far.
As I've mentioned, this is all moo & theories. Just my guess.