"I'll kick myself in the teeth if I cannot deliver the update by the end of this month" is neither a promise, nor a wishful statement (i.e. "I'll try" or "I hope"). Metaphorically, she is saying she will punish herself if she does not manage to deliver the update before September ends, which strongly suggests she must deliver it by then, as no one would want to inflict physical harm on themselves. So while it is definitely not a promise, it certainly means you can expect it to be delivered before September ends, or thereabouts, as to avoid the undesireable consequence. That's it, end of story. No one is right and no one is wrong.
Either way, though, one can hold two thoughts in their head at the same time. You can claim that an update should in no way be rushed into completion, and simultaneously believe that four months is way too long to deliver it. I certainly don't think she should rush it now - she might as well take a few more weeks to get it done properly, but I also think she has some serious thinking to be done for the next update. We could very quickly get to a point where this game is progressing extremely slowly, especially considering that the dual protagonist set-up is not likely to make the number of possible variations fewer the longer it goes on.
I was very surprised when Eva made that choice, as the consequence we are seeing now would be possible for anyone to predict. It also has terrible synergy with the stat-system and the sub-par save compatibility; the stat system requires extreme precision in your choices, which you forget during the long update times, and then you cannot load up an old save to not have to think about it. Eva is in serious need to either reconsider the scope of this game or hire some more help, as this, as I mentioned previously, could risk getting out of hand very quickly.
