I like Linea. It is original and very easy to say.

Maia, while the meaning seems perfect, I hear the name a lot (different spellings, but same pronunciation), so I would consider it too common. As with Luna, becoming common.

Nyx is too harsh sounding for that sweetie, and Nemesis is too many sylables.

Vala is OK and so is Helen, but Linea is just SUPERIOR.

(my opinion)