Should we use comma after "after a while"? For example,
After a while she stopped thinking about him.
As it's an inversion of 'She stopped thinking about him after a while', the comma would help make the sense crystal clear. Compare a more ambiguous sentence:
She stopped thinking about him after the event.
If you invert it, it becomes less clear:
After the event she stopped thinking about him.
Is that ...
After the event, she stopped thinking about him.
or...
After the event, she stopped, thinking about him.
Commas clarify meaning, particularly in sentences where the standard order is inverted.