Yuri Project
joined Jul 14, 2016
The literal translation is "The kouhai-chan from after graduation ♡" (卒業した後の後輩ちゃん♡), but that sounds awkward in English. The "cute", "we", "left behind" are not in the original. I haven't read ahead, so this nitpick might be completely irrelevant, but it's important in the sense that we shouldn't start speculating based on translation word choices.
The meaning is not "from after graduation"; a "literal" translation would be something like "after-I-graduated-kouhai-chan." In Japanese, generally there are a variety of possible ways an attributive clause interacts with the head noun, but it's usually clear in context. In this case, "the kouhai I graduated from" or "my old kouhai now that I've graduated" seems like the obvious meaning. My word choice was based on that interpretation.
As for the "cute", I needed to use "kouhai" as a noun rather than as a name or term of address because of the way the statement is structured. I try to only use honorifics on terms of address, and ideally only on actual names: "the kouhai-chan" just reads very poorly. So I wrote "the cute kouhai" instead, as it conveys the same meaning and feeling; the "-chan" here is basically a term of endearment.
The "we" is a bit of a guess. It's unclear who she's speaking to, since we can only see one side of the conversation. Based on the way she's speaking, I thought she could be talking to a friend from high school who'd graduated with her. Probably someone who stayed in or around Tohoku, whereas she herself went to university elsewhere.
Generally, I think you're right. If the translator is very good, then you can read a lot into their words about implied meanings in the text. If the translator is like me, then sometimes we fail to consider potential alternate readings of our words (or just screw up) and accidentally imply something that is incorrect. When a statement is ambiguous or has multiple meanings, it's very hard to properly convey those hints or alternate readings in a different language.
I wrote this translation after I already read the next couple volumes, so later events influenced how I resolved ambiguities in the text. I believe I remember thinking this was Igarashi when I first read it, but maybe it's not as obvious as I thought.