Comma rules for sentence adverb placed in the middle of the sentence

Why writer has not used comma before or to join these two independent clauses.
"Had anyone actually told her that or had she merely assumed it?"

Solution 1:

You're right. Using a comma after a coordinating conjunction, like "or," when it introduces a second independent clause, like it does in your example, is standard. You're never wrong to do that.

However, grammar does provide that if both independent clauses are "very short," then you may forgo the comma. Of course, the precise meaning of "very short" is unclear. That makes the length of "very short," to some degree, a judgment call.

If we are giving the writer the benefit of the doubt, then we would presume that the writer surmised that those independent clauses were both "very short" and so felt it appropriate to exercise the option of forgoing the comma.