Much as Ellisaria dislikes the intimation of weakness, she dislikes being impaled on a mountainside even more. Her human form is simply more subtle, and thus better suited to evading the gronn.

Unfortunately, it is also conveniently sized to be eaten in one gulp by the mirror-faced snake (what) that comes out of literally nowhere.

At least she is alive to be indignant, even if she's no longer in Outland.