tl;dr if her time in the village would be extended, there would be more room.Selena isn't a side character. She is the goal of your quest, ie. the target at the end of it. The entire point is that she won't arrive until late and that you're preparing for this event. What possible situation could you imagine where there would be room for more scenes with her in the current storyline? From the moment she arrives in town, her timeline is packed. I'm sorry, but I'm struggling to understand what your point is exactly. I mean, why ask for more content for her when there is literally no room for it?
I think if the coronation ceremony and the festivities are extended to about a week or so you could have opend a whole new part of the game where the game/gameplay is really about the princess/queen and exorcising the Demon. It was totally normal to have week long parties at such events so why not take advantage of it. There were still traces of here, at least years back so why not give the chance of appealing to her by charm and/or magic of a longer course of action while staying hidden with your skills so that the demon is weakend and blindsided?
At the moment you get steamrolled at first sight, running around a couple of hours looking for her, fuck her, do a Detective Conan on the Demon and Thaddeus and GG.
It just feels like a good series where its (against all fans) canceled in the 3rd season and they just need a fast and some kind of plausible ending.
Hope i could somehow elaborate what i thought about more content
Kind regards!