??

I believe that’s a very objectiv and realistic way to look at it. But Biance hasn’t forgotten her first life, and the feeling of desperation and hurt being on her absolute lowest still haunts her. She was granted a chance and chose to write the victorious history she didn’t get in her first life.
My guess is it didn’t occour to her there’s always losers where there are winners. She felt horrible knowing she had a hand in the princess downfall, and had «doomed» her into the same life she previously experienced.
I’m pretty sure she would do the exact same things all again if given the chance to; it’s not like she regrets it.
But feeling upset that her happily ever after did not include anyone, wondering if there was anything more she could’ve done earlier, and taking the responsibilty in changing fates for both good and bad with the powers she got; for me it’s a wonderful touch to the story. They never include this to other turning-back-time stories. It’s a «with power comes responsibility to it» twist, and her having empathy to the case makes her much more humane and a good Saint. These are my opinions!

Bravo!!! that's a great observation

Nah, I totally get what you're saying and I agree that she prolly felt some sort of sympathy for Ms. Red Head, but I'm coming from the angle where realistically there's prolly hundreds/thousands of people out there whose life turned out worst because of Bianca's decisions.

What I mean to say is that this whole arc was nonsensical to me. Can you imagine if they wrote a story each for the hundreds of people whose lives got worst because of the war? Why did they randomly introduce someone new for a meh B-plot? They teased it as the two knights potentially finding romance, but ultimately it was just some lady's backstory speed run. The entire thing made me feel like "So? Why should I care about this character when she doesn't even exist in the actual plot?"

I'm sure you can argue that it fleshes the story out more and gives us details of all the things that happened during the war and blah blah, but for me side stories are more fan service/au/epilogue stuff that focus on the leads.

I don't think it was meaningless or uninteresting. The princess of Aragon and Bianca are considered parallels (women of high standing who had to marry for their houses---and had an affair out of loneliness). They're two sides of the same coin who's fates got flipped. Whether for the better or worse.
Since we read this story weekly it's difficult to remember all the details but she was briefly introduced in chapter 24 (much like Yvonne's sister was also briefly mentioned in the early chapters). I think it might be harder for readers to care unless they read it all in one go; but I personally thought it was a good side-story. The romance with the knight was just a pretext.

That's fair and I respect that. I just personally found it less interesting that other potential side stories.