Despite her recent difficulties, Rachel understands the power that she, Frigg, and her sisters all wield about as well as anyone. She knows a lot about the different forms it takes, the different things it can do. So she looks at the change in Hestia’s eyes in panel 5 and realizes what is about to happen.

We did our best to leave that ambiguous here. From the script: “Some readers might be forgiven for thinking Rachel’s afraid of losing, afraid that Hestia’s powering up for a final assault.”

We also had a bit where Rachel used her powered-up strength to tear one of her sleeves off before the flames on it could do her serious harm. Ah, trying to balance steady flow, fast pace, and tactical details in fight scenes, always a challenge.