Aremis was clear ahead up until she passed head-to-wind. At that point, she was tacking, and became the give-way boat. See Rule 13.

You can't just tack right in front of another boat, no matter how close to the mark or the layline you happen to be.

It appears to me that Artemis did indeed complete her tack just prior to contact. Since Groupe Edmond had long since taken avoiding action (albeit unsuccessful), A had already broken RRS 13. Completing her tack just means that she broke rule 15 as well.