Yes, I can also see them planning this and purposely leaving Wendi out of the planning with the goal of (obviously) never getting caught and thinking it will simply be an unsolved crime and never disclosing the truth to Wendi. As you suggested, the plan could have taken a turn at any point for multiple reasons and we don’t have enough information to be certain, we can only speculate. Did Wendi figure it out, were they forced to tell her as some point – day of, shortly after? I will continue to say its surprising to me that so many that follow this case say they would never have planned this without Wendi’s blessing. A psychopath doesn’t ask for permission when they are doing something they think is in ‘their’ best interest or the best interest of their family – even if its murder. It’s hard for a healthy human mind to wrap their head around why they didn’t need her permission.
As far as Donna’s message "your brother protected you for years". We can look at that statement in multiple ways. Two likely possibilities:
1) In Donna’s warped mind, the plan to murder Dan was done for Wendi’s best interest and Charlie did it to protect her.
2) It was a more general statement to mean that for Wendi’s entire life Charlie protected his little sister.
I personally think it had more to do with something in the ballpark of two above. Charlie was the first Adelson accused and at the time of her statement, the only one that had been arrested and he had already been convicted. IMO, nothing Charlie did (that is public info) in the aftermath of the murder was done to protect Wendi. I think Donna was saying and doing what she does best, applying the Jewish guilt because she felt Wendi abandoned them and in Donna’s warped mind she believes what they did was justified and Wendi doesn’t appreciate it. Donna is a really sick person.
Unless they find more evidence, the ‘this is so sweet’ text and deletion will likely be the most difficult hurdle for Wendi and her defense team if the day ever comes that she is on trial. IMO, it doesn’t prove her direct involvement, but the fact that she wrote that and deleted it is not a good look and many will interpret it exactly like you suggest unless more details are given like what may have preceded that text from Wendi. Was it in response to something Charlie had texted her? If it was just a random text with no other context in the text string, it does not look good. One of the challenges with trying to apply common sense or logic and speculating on the case is we are only given certain details and set of facts by the prosecution. If there was a message from Charlie in that text string that preceded Wendi's text and it was unrelated to the murder, maybe something else that could have prompted such a reply, would the prosecution have disclosed that?