I looked it up in online dictionaries and they didn't really prove useful. "Selfish" or "convenience" doesn't seem to fit.
So this is a quote from Niji-iro Tohgarashi
This is the sentence a brother said about his sister, after he found out that much as she hated insects, she seemed to like fireflies (which are insects), a lot. I figure what he means is "she hates insects, yet she likes fireflies which are insects, so she's kinda self-serving in a way, likes what looks beautiful and hates what doesn't". But "selfish" sounds a bit misleading/confusing, and harsh, and I'm not sure about the connotation of "self-serving" either.
Yet, the same word is used later
In this case, it describes the way people classify insects and grasses into categories like pests and weeds to their liking. They like what's good for them, and hate what isn't. In this context, both "selfish" and "self-serving" sound apt.
If both of these contexts were independent from each other, I would go with "Whatever suits her" with the former sentence, and "The selfish means" with the latter. But they are not independent within the bigger context of the manga. And both sentences use the same word. So I wonder is there a good way to describe those similar qualities ("a little self-serving, but not that serious" and "it's self-serving and now we're talking seriously") with the same word(s) in English that will sound natural and soothing for both sentences.