Going to change the translation of the artist's commentary, if nobody minds. If somebody finds my translation inaccurate or I've misunderstood something, feel free to correct it.
先輩のことだから "Because it's senpai" would be a more literal translation; "Knowing you, senpai" conveys the point in more natural English, however, so I'll leave it be.
どーせ1人寂しくローストチキンでも食べてるんじゃないか Anyway (どうせ), one person (1人) would be eating (食べてるん) a lonely (寂しく) roast chicken (ローストチキン) or something (でも), isn't that right? (じゃないか)
と思ってからかいにきました So (と) I thought (思って) I'd come tease [you] (からかいにきました).
What's interesting about karakai (からかい), to tease or pick a fight, is it etymologically speaking has this connotation of getting tangled/bound up with the other person. Although "tease" would definitely be the standard translation, I wanted to preserve this undertone.
For it to sound as natural as possible while conveying the original meaning, I'm putting it like this: "Knowing you, senpai, there'd be one person eating roast chicken all alone or something anyhow, right? So I thought I'd come tango with you."
For those not in the know as to why the roast chicken is significant for Christmas: https://www.smithsonianmag.com/arts-culture/why-japan-is-obsessed-with-kentucky-fried-chicken-on-christmas-1-161666960/ Despite her putting on airs, she's the one who brought a roast chicken. This is why I feel it's necessary to retain the ambiguity of 1人. Even though you'd naturally think she's just mocking him, if you read into it a little, wouldn't she be eating that chicken alone if her senpai can't be expected to come to her?