Dinah doesn't think that things need to be bad to want a teacher. She'd never turn down a teacher, even here in Keeliai. Especially here in Keeliai, really, with the range of other world styles available to her. It gives her pause, that Korra needs to think she's bad at something to benefit from a teacher.

But when she says yes, the frown disappears.

"Then I'll be your teacher."

And all that means, from helping her improve her existing bending skills, to taking responsibility for her use of those skills, to helping her face her fears and being able to hold her own against chi-blocking.

And as far as Dinah's concerned, that's that.