It does not come across as self-sacrifice to me. At least, that's assuming that nothing untoward comes for Hotaru by taking the place of Kyouko.
It just seems like Hotaru well and truly is the kind of person who would go to bat for someone else in need, regardless of what that might cost her.
And, I kind of wonder if her death coincides with her getting into a fight with Shiori over her unselfish nature. If that fight with Shiori was Hotaru denying her heart in the most severe way she ever did, by effectively giving up on Ren for Shiori's sake. And Shiori, for her part, was upset at Hotaru for doing exactly that: taking the fall, "losing", stepping aside for the sake of another's happiness at the cost of her own, and in that moment she had the supreme misfortune to die in that bus accident.
It would certainly be poignant, if so.
Thanks for the TL. Nearing the finish line, and I'm curious to see how it all turns out for Hotaru.