The drive to the crime scene is the overt act that demonstrates WA was part of the conspiracy. Case law supports this. Australian case and not a like for like comparison, but NSW v Rubasha. The perpetrator was convicted of guilty of conspiracy to rob while armed. All he did was scope out a house he was planning to rob. He didn't plan to rob it on that day. He participated in an act that furthered the conspiracy. There are similar US cases, a bank robber in Florida was convicted in a similar fashion. Both these cases I suppose they could argue they had not committed a crime, they were just driving, vis-à-vis WA's drive.
However, its what the jury believes to be the case. It's not going to be hard for the State to show that WA's drive was to check out the crime scene. Ultimately she lied about it, which destroys any kind of legitimacy about her shortcut. So if hypothetically she knew Dan had been shot and drove to the crime scene, that's still not part of a conspiracy. But then the volume of communication between her co-conspirators on the day of the murder, plus all the other evidence including statements to JL confirm beyond a reasonable doubt she knew CA had planned to kill Dan.
Her act of driving to the crime scene to confirm Dan's death is conspiratorial, as it constitutes the final step in executing the crime and ensuring its completion.
Note you are using words such as proof, evidence, willingly - looking for the proverbial smoking gun. There isn't one. There is no text from WA to CA saying "I am now driving up to the crime scene to make sure the hitmen we all hired did their job and killed Dan."
Trescott is supported by other seemingly inconsequential evidence that all support and strengthen one another. e.g You and others often dismiss the validity of JL's statement, but it should be considered with all the other evidence. Similarly with her phone call with CA. He is her beloved brother, they often spoke on the phone, it means nothing her lawyer would argue. Except the phone call was purported to discuss a broken TV, it went for 18 minutes, it happened 45mins(?) before the murder and the call was to a convicted co-conspirator.
A jury is not going to believe the call was about a broken TV.....