"Αυτή δεν έχει καθόλου αδέλφια."
Μετάφραση:She does not have any siblings.
"she does not have any siblings at all" is currently marked as incorrect. Unless my understanding is a bit out, this is a valid interpretation, καθόλου making the sentence a bit more emphatic than "αυτή δεν έχει αδέλφια"?
No, your understanding is not out.
She doesn't have siblings/has no siblings - Δεν έχει αδέρφια
She doesn't have any siblings/has no siblings (at all) - Δεν έχει καθόλου αδέρφια
So yes. You are correct. It's noted, thank you for your comment. ^.^