Same issue!
Oh wonderful! I didnt know there was a walkthrough. So according to this, I should have Marena fully unlocked, but she isnt. I've reached End of Content with every other character, and spent plenty of nights in the bedroom boosting stats enough to hit the cap. I'm wondering if something is missing here? Is there something you have to manually trigger after reaching EOC with the other vixens to unlock her? I feel kinda dumb cause it seems like she would be integrated back into your fold first rather than last.