I really do hope that Rua eventually does redeem herself. But I imagine this won't happen without outside intervention. Honestly, I'm hoping that her grandfather realizes how much his doting is hindering her true happiness and indefinitely disowns her. Maybe give her a small apartment, an allowance that if budgeted well can give her three cheap meals a day. Tell all the people that work for him to stop treating her like a member of the family. Make everyone in the entertainment industry stop trying to push her and tell the critics and journalists to be every bit as critical of her as they would be of a rookie that just started out. Keep that Rei kid with strict orders to only prevent extreme, explicit threats to her life and kidnapping attempts, but nothing more, and make sure she understands thoroughly that she is not to take any commands from Rua. Obviously eliminate that scholarship.
And of course explain to Rua that what he wants is for her to learn to stand on her own two feet without him holding her up. That if she can't manage that, there is no way Kazuma will even be willing to consider her a friend, let alone anything more. It will take her a while to really grasp how hopeless she is without her family, and probably even longer before it occurs to her that this way of life is actually normal, that everyone around her has had to live this sort of life every day since they were born. But if she can learn this, learn what it's like to see things from that perspective, then maybe she'll be able to at least become an actual contender in the fight for his heart rather than just the "pig" that ruined his life.
I seriously would love this story if it does this, and I get the feeling at least something mildly similar will happen at some point, as it really doesn't look like it's going to be one of those series that just crushes the villain and forces her to leave. Makes me wonder though whether there are any series where instead of the hero cutting ties, he tries to change her. I've seen plenty of cut ties stories, and stories where the guy decides to get revenge on the girl. How about one where he tries not to hurt her, but to force her to see the truth? It'd definitely be a difficult task, but seeing the hero break the girl's illusions, force her to see the truth, until she has no way to maintain her entitled sense of justification would be entertaining in its own way, and in some ways could be even more intense, harsh and cruel than your more typical revenge.