Yeah. She regains relevance back in the Magic God Othinus arc, but you know. It's probably not going to be animated within the next few years anyhow, so you might as well read it yourself.
On the note of Raildex, I'm surprised Kamachi actually finds a way to integrate what are supposedly anime-only story arcs into the LN. Like... Therestina is officially acknowledged as a Kihara by the invading Kiharas during the Baggage City arc (particularly by Enshuu, who, as a Kihara... Well... You know the deal.) Furthermore, all the crap Harumi went through to save her students is canon, which is pretty dang great.
(On the note of things to come: You remember Hamazura from the end of Index II? He becomes a very important character in the near future.)