Need hello for a christmas gift

Hi everyone,

I was looking at possible christmas gifts for my GF, we watched together the anime and she really loved it.

So I was thinking on gifting her a couple of volumes of the manga.

But when I looked at it I was a bit overwhelmed there is a web and a light novel? And 2 mangas telling the same story? So maybe you could help me.

Seeing that the S2 anime will start soon again, maybe is better to gift her what we already watched and watch S2 together, or maybe there is a spinoff.

What would you suggest me to gift her?

Manga or Light novel? If so which volumes?

Thank you!!

Sorry if it has been asked before.