Well, now you're nitpicking, and I think the "controlled by her emotions" part of the quote makes it pretty clear what I mean by "irrational" in this context.
Of course Lena has reasons to distrust Cherry and treat her actions with suspicion. That goes without saying. If Lena's goal (consciously or unconsciously) is to get a complete understanding of everything that happened and whether her judgement of Cherry's character is representative of her in general, the rational thing would be to talk to Cherry and listen to what she has to say. If her goal is to get over it by allowing herself to be angry without taking in all the nuances, as well as limiting her contact with Cherry and Axel to a minimum, it's obviously rational to not bother about what she's got to say.
I don't really care if we're calling it irrational or not, but the point is that Lena's seemingly not interested in getting a more complete understanding of the whole situation, and/or her strong emotions get in the way of it. I'd probably react the same way myself, but as players we know that Cherry's perspective adds nuances to it, and also gives us good reasons to believe that she actually is genuine about her regrets.
There's in other words a clear discrepancy between what we as players have seen of Cherry's character, and what Lena's seen—at least partially because of how Lena relates to all of it. The topic I was discussing, was the possible future developement in the relationship between Lena and Cherry. In that context the discrepancy is clearly interesting. Considering how Lena and Cherry are getting drawn into the same group of friends, they'll likely end up talking about all of this at some point, be it through a confrontation or in more civiliced forms. If that happens, I assume it'll include the option for Lena to take note of Cherry's perspective and adjust her own—with whatever consequences that might include.