I think she is asking specifically about the grammar, and why it is "better late than never" rather than "late better than never"
In this sentence, the subject is omitted. It's not just a comparison saying that late is better than never, it's saying that the state of being late is better than never. For instance, we could lengthen the phrase and say, "it's better to get it done late than to never get it done at all"
Do you understand now?