A couple more things about boosting your relationship with Welles: Having a high reputation when you first meet Welles means she starts with a favorable impression of you, which is the equivalent of a very significant boost. (Participating in the Forlorn Hope is helpful for this, but not necessary.) During second Kharangia, you get a significant boost if you go to help the Second Battalion of 5th of Foot and directly reinforce the line, especially if you follow her directions.
From a min/maxing perspective, it seems possible to disagree with Welles at the dinner (thereby meeting the king) and spend your free time at Mhillanovil doing something else (mentoring Renard, continuing to write your memoirs, and refining your Antari are all good choices), and still end up with a high enough relationship that you might end up marrying Welles. Try following the instructions in the spoiler text above, say that her proposal is admirable but impractical, and at second Kharangia don’t say “Are you sure you would rather not observe from here?” (You don’t need to visit her the night before the battle.) You should end up with a relationship value of 70, which is pretty high, though it might not be enough. You also won’t have expressed romantic interest yet, though I imagine Lords isn’t too late for that. Of course, even if an anti-feminist war hero impresses Welles enough to marry her, I imagine there will be significant conflict in their marriage.
From a min/max perspective, capturing Princess Anna (provided you have the stats to do so) is almost strictly superior to killing Lady Aleksandra. Aside from being a despicable choice, killing the girl means you lose Anna’s ransom money and suffer penalties to reputation, morale and loyalty. The only advantages to killing her are a significant boost in your relationship with Katarina, and you repair your relationship with Lefebvre if you had previously reported him to Hunter.
Note: while I often mention min/maxing, in my own playthroughs I blend role-playing and min/maxing. I have 4 characters, and I try to balance (i) keeping them distinct, so that I can explore various interesting parts of the game (they’re all from different regions, are different ages, have different personal stat strengths and weaknesses, and have different sergeants in Guns; one is a deserter, one doesn’t do the forlorn hope, two participate in the secret mission, etc.); (ii) having their choices fit their internal motivations and values (which can change over time); and (iii) min/maxing within that framework. Even for the characters whose values don’t match my own, I want to feel some sympathy for them so that I can get into that mindset and role-play that character. While I can understand why a character might do it, I don’t want to role-play a character who kills a 13 year old non-combatant girl in cold blood.