Years ago my ex told me about a girl he'd dated when he was late teens / early twenties. He knew it couldn't go anywhere but she was really into him. So when he ended it, he didn't just end it. He said he ended it and made sure she'd hate him. His reasoning was this was kinder in the long run because if she hated him, she'd get over him and move on. He's an idiot but he's not a jerk so it was surprising to me that he did that. I've never asked him what he did to make sure she'd hate him, but we have people in common so I know for a fact she's alive and well.
My point is if I was on the receiving end of those texts, I'd think he was going to hurt her feelings / embarrass her so she wouldn't be around anymore. I'd tell him forget it, just stay away from her.
I'd also probably roll my eyes and assume that he was just trying to trash her to me so I wouldn't be threatened by her and would quit being upset with him.
This was almost a year before Tim Bosma and as far as we know prior to Laura, Millard didn't kill anyone. And, there was no reason for anyone to think he did or to think he would kill anyone.
I'd say maybe there's more that we haven't heard yet that's more incriminating towards Cristina but I doubt it or more charges would have been filed against her.
That said, if I were to get a text like that and then the subject of that text were to mysteriously go missing I would stop and think 'hmmmm....'
But Cristina seems as narcissistic as her ex, so given that the issue of Laura missing wasn't about her, I wouldn't be surprised if it didn't register with her.