Player wants to skip other players' backstory arc

My players are having heated disagreements about which plotlines to pursue. I'm 12 sessions into DMing a campaign with 4 players, all of which are new to d&d except for the barbarian player (and myself). I am close friends with everyone involved and would like advice on remedying this issue without removing anyone from the group. Recently, the party has started butting heads about battle tactics to the point that it was upsetting multiple players, in particular the sorcerer player, so I spoke to her individually abut it. She shared that when their characters argued about in-game issues on anything from tactics to bigger story choices, it would really stress her out irl and she wanted to avoid it. This was disappointing because I love throwing tough moral dilemmas at my players and watching them debate, but I didn't want to keep upsetting one of the players, so I've since made a point to structure the storyline in a way that always presents one very enticing way forward that I imagine every player would agree on, thus no intense debates.

For context, the party has mostly stuck to their starting city so far and has 3 currently active plotlines based there. I personally love a nonlinear narrative where they solve each plotline in parallel and discover secret connections weaving them all together rather than straightforward episodic stories. Last session, one of the plotlines temporarily brought them out of the city and to the hometown of the cleric to retrieve a rare ingredient. When they arrived, they found that the barbarian's warlord nemesis had just invaded the town, killed some of the cleric's friends, and made off with important valuables. I figured the party would jump at the opportunity to go after this guy and get some well-earned vengeance for not only 1, but 2 party members especially because his army had been decimated and he was temporarily vulnerable. However, as soon as some of the players began planning to pursue him, the sorcerer player shut it down and said they should just get what they came for and head back to their starting city. Her in-game reasoning was that she didn't want to waste time and risk them failing their original mission (which had much lower emotional stakes). Her out-of-game reasoning was that she felt stressed that they've already taken on so many plotlines and didn't want another open one, especially one that "sounded combat-heavy" since that's her least favorite aspect of the game. The barbarian and cleric players were obviously upset because they felt like skipping this plot would make their backstories irrelevant and they were both emotionally invested in a satisfying conclusion. The barbarian also noted that combat is by far her favorite part of the game and didn't think it was fair to skip past this when they've already spent multiple sessions on a more social plotline related to the sorcerer's backstory. I want to do everything I can to avoid irl conflict and remain neutral about party decisions, but I can't help but feel like the option most fair to everyone would be to finish out this warlord plotline, including fair to me since I spent a lot of time preparing it. Of course, I couldn't point out that the next session would end with a fun social element and a big plot twist sending them back to the starting city.

We ended the session and decided to discuss it next time. Since the sorcerer player is going out of town soon, I also offered to have us play the session without her while she's traveling, so she could just rejoin the next session once it's wrapped up, which she seemed open to. Granted, the other players were still a bit upset that she'd rather sit out than play through their backstory plots. Someone also offered splitting the party, to which everyone in unison yelled "NO!" Not sure how to proceed, just thought I'd gather y'all's thoughts on everything! Thanks!