Technically, "I had not seen it yet" would be "Ještě jsem to nebyla viděla", but this pluperfect construction has been obsolete in Czech for about a century. It's still correct, but archaic. So nowadays, "Neviděla jsem to." can be either "I haven't seen it", "I didn't see it" as well as "I hadn't seen it".
That's a very different meaning than we have here. "yet" at the beginning means something quite different from "yet" at the end. Your sentence would translate to "Přesto jsem to neviděla", for example.
"Ještě jsem to neviděla" means I haven't seen it yet (I'm probably planning to see it, but so far have not seen it), there's no comparison to others involved.