I suppose that from a certain point of view you could view it as some kind of betrayal, but when did she ever make any promises about this sort of thing (for that matter, did she make any promises at all)?
We have agreed to keep the peace in the outer sect in exchange for stones every weeks, as well as having minions and some other advantages.
Anyway, rereading the update a few things strike at me that I had either missed or not talked about.
First, Chu Song is Mountain and Thunder. Those are somewhat opposing element, but what it means is that she should have some sudden explosive power and speed, but not long lasting. However, she should have some incredibly tankiness.
Second, I think I had misread what Chu Song said: she didn't quite say that she will stop us by talking, but rather that she will stop and and talk to us. I already suspected that she was hidden to make sure we weren't leaving, and then planning to talk to us when it was too late, but it appears that we might have a bit of time before things begin. I think that just means running away quickly is even better though, as it means getting to friends before they are in danger, and not in the middle of a battle.
Third, she got angry when the idea we were loyal to Cai came to her (talking dangerously), and she immediately painted it in the worse terms she could probably come up, with 'playing a loyal dog'. She very likely really has some enmity with Cai.
Fourth, the fight option has Ling Qi thinking 'Winning would put her out of commission for the day'. As in, Ling Qi thinks there is a real chance Chu Song would be a pain for the rest of the day if she doesn't take care of her. There is possibly a bigger chance than I thought of Chu Song attacking our friends to stop us, or something like this.
Fifth, While Ling Qi is worried talking to her means Chu Song can stall us, she is also wary of having possibly being lied about Sun Liling. I don't think her lying about it means we should change our plans, but this and Ling Qi having caught Chu Song before Chu Song wanted to be caught means that we probably can talk a couple minutes before having to run away.
So, here is what I think upon re-reading:
Fighting give us a long shot of taking care of Chu Song before the ruckus starts, but we won't be able to get to our friends before they have begun fighting.
Running now means using resources before the ruckus, but it might mean getting to our friends before it begin.
Talking means we will either have to fight or escape or 'something else' later to get away, but it means having a more solid understanding of what to do then. However, this come at the cost of being with our friends before the ruckus begin, or even it being well underway if we have to fight her to get away.
So yeah, upon further thought while Ling Qi thins the girl is trying to stall us, having caught her early means there is a decent chance of having a bit of breathing room before the event happens. So this vote
might be more about how to use that breathing room (taking out an opponent, getting to our friends before they are ganged upon, getting more information). Or I am completely off.