Eliza realized something as she saw Eren transforming into a dragonoid using his Hex Artifact Set.
She realized that Eren had been obsessed with countering her in every possible way. He had always planned to face her after her rebirth in a new vessel. Because the dragonoid transformation wasn't something that could be unlocked on a moment's notice.
Although the Dragonoid transformation that Eren had tapped into was done using the artifact set, Eliza didn't feel that it was an inferior and shoddy copy of what she could do as a genuine dragon half-blood. Rather, she sensed a strong mana signature from Eren, allowing her to know that Eren had outdone even the most established artifact creators of Anfang.