I can only tell you how I’d handle it. I would bring one of her siblings in to keep her company. Brood them away from the mama, since this teeny one is behind. Then, you could grow the 2 out together, and introduce them to the flock later. Your chick will thrive with a sibling, rather than...
Sometimes, an assisted hatch takes a little longer to get strong. Experience tells me that. I just had a Serama pip at the small end of the egg, and it had totally exhausted itself. I assisted (something I never take lightly). The chick mostly slept for the first 48 hours. Now, you wouldn’t even...