Look, from what you're saying, online system yes? If so, then system saves what you did, then separately when she continues, saves what she did. separate IP addresses, changes would be tracked and assigned to the individual IP address.

If she gets audited, they can see what was done on your computer, compared to hers. Do yourself a favour, check your IP address (just google it on your computer) and then go and write a statutory declaration that says exactly what you assisted with on your computer. State that she stated you're wrong on the bonus needing to be declared and took over doing it herself at that point.

If it's not an online system like that, then do what others are suggesting.

But if it is, it's not nearly as complex to prove, because if they approach you about the information being incorrect, you can then show your IP address and stat Dec, they can check it and verify what you're saying, meaning you'd be all clear unless she fights it with her own stat Dec. If you think she may do this, then back it up with recordings.

What confused me about that is, had she brought something up before about weird behaviours or is this the first time? Had sexual history ever been a discussion between these two? Past partners etc?

I may be overthinking it, but I've always been someone who has these discussions early and found that it works out well for me.