Wind Walk.

If Merrin asks why they didn't do this earlier and instead of getting her injured, it's because Esta has never cast this spell before, and Esta was leery of messing with his 6th-circle slots under poor prayer communication conditions.  And not at all because Iker Egobar had helpfully mentioned to Esta upon his attaining 6th-circle that everyone would be incredibly unimpressed with him if he found some flimsy excuse to cast Wind Walk, and Esta had very nearly managed to forget the spell existed.

Wind Walk.

If Merrin asks why they didn't do this earlier and instead of getting her injured trying to ride a tidal bore, it's because Esta has never cast this spell before, Esta didn't realize how much danger she was in, and Esta was leery of messing with his 6th-circle slots under poor prayer communication conditions.  And not at all because Iker Egobar had helpfully mentioned to Esta upon his attaining 6th-circle that everyone would be incredibly unimpressed with him if he found some flimsy excuse to cast Wind Walk, and Esta had very nearly managed to forget the spell existed.

Wind Walk.

If Merrin asks why they didn't do this earlier and instead of getting her injured trying to ride a tidal bore, it's because Esta has never cast this spell before, Esta didn't realize how much danger she was in, and Esta was leery of messing with his 6th-circle slots under poor prayer communication conditions.  And not at all because Iker Egobar had helpfully mentioned to Esta upon his attaining 6th-circle that everyone would be incredibly unimpressed with Esta if he found some flimsy excuse to cast Wind Walk, after which Esta had very nearly managed to forget the spell existed.