Does having a non-swimming tail help with using a swimming tail? [Which might not be the most elegant way of putting it, but "swimming tail" seems to her to sum it up well enough.]

Exactly. Just test this shit out, see some cool fish, don't get our lungs crushed by a metric fuckton of water.

[That said, there's no way she isn't going deeper later. But that's after some practice, okay.]