In English, I'd guess I-na like the pronoun. Other languages, it'd be EE-na; and in Afrikaans also EE-na but the EE is a shorter sound than usual.
I've known plenty, and it's always turned out to be either a nn for something with that ending, like Katerina, or a full name on its own, given to honour someone called Katerina or something similar. I find it a bit flimsy.