AvangiHi sd15, Welcome to the English Forums. I'm afraid all our gurus have gone home for the night.
I agree there's no grammatical justification for the comma, and I agree that you have a compound predicate.
I'd take the comma as an optional stylistic pause. Would that be semantic?
If you want the feeling, "She ran to the end of the field without looking back," surely, no comma. "Never" is way more dramatic. Does this come at the end of a paragraph? - a chapter? You could even use a dash.
I think the comma here is just another tool the author uses to play the reader, one way or the other.
Best wishes, - A.
Most authorities consider it error to use a comma where none is authorized. Only opting against an authorized is a matter of style. "Optional stylistic pause(s)" must have reasons, exhausted by syntax and semantics. Some linguists say the comma is governed entirely by semantics, but I'm not even sure whether the distinction between restrictive and non-restrive relative clauses is semantic or syntactic.For my example, I haven't seen any rule that clearly authorizes the comma.
Your example, "She ran to the end of the field without looking back," doesn't change the writer's option for comma use, as that string could appear as "She ran to the end of the field, without looking back." But the prepositional phrase, "without looking back," makes the option understandable: you can treat "without looking back" as parenthetical or not, depending upon the intended emphasis. "

nd never looked back," on the other hand, can't be a parenthetical phrase or a restrictive clause, when the string isn't a phrase or a clause.
From these considerations, I conclude that calling the construction an "optional stylistic pause" is just euphemistic for error, although an error committed by educated writers and even professional editors.
I wasn't thinking of any particular role in a document, but my remarks consider only non-fiction. Maybe there's room for "optional stylistic pauses" in fiction, where even the frankest grammatical error can be justified.