Well, you can pretty much skip her if you have Hina and some good duelists. Not saying everyone does though, but there are a ton of good choices that beat her.

Honestly, she is probably the worst collection black. I know people tend to hate on Liana, but Nagi is just so blatantly much worse in comparison. At least Liana will help you if you lack paralyze immunity. Nagi's only strength is against youkai and the fact that she becomes a decent duelist with SAW, once per battle.

For me personally i see no use in her for me, ever, so i won't do more than natural regen + perhaps a few SC on the second week when it's a new month.