A weird one cause absolutely nobody knows nothing about either character. I'll shed some light on Oksana, what she does.
Oksana's main method of attack is firing bolts of energy at her opponent. Her weakest, the White Bolt, are powerful enough to destroy a church roof, her most powerful, the Divine Bolt, one-shot
this guy, and severely damaged
this guy. And she has some AOE attacks too, Holy Storm damages the entire opposing party, and Sacred Burst attacks a clustered group, damaging up to 13 foes.
She is a glass cannon at 8-C, if Nonako can open the battle with a ranged attack immediately, she should be able to one-shot Oksana. But, Oksana does amp herself with Celestial Drive in character relatively quickly, so that shouldn't be a problem for long.
However, in hand-to-hand, Oksana isn't very impressive. She tends to smack and bash with her mace, and as that is only Small Building, Nonako should be able to shrug that off with ease. Besides, Oksana isn't that skilled close up.
So, with all that, there are three ways I see this battle going (Bear in mind I know very little about Nonako).
1. Nonako one-shotting right off the bat with a ranged attack
2. Oksana amping and teleporting around the battlefield, firing energy bolts at her leisure
3. Nonako trapping Oksana in H2H and dismantling her
Let the debate begin!