docs:
Resize events are sent to widgets that have been resized.
So I would not assume that sending a QResizeEvent will resize a widget.

Moreover, being "lucky" on height() etc is not something I would want to depend upon.
I suggest you just (if nec. create and) call the appropriate slots on the widget.
If it is just one widget (maybe your own class): easy. just add the slots.

If it is a widget with "closed" source (for you), you can create a helper class that has those slots and then forwards the calls to the widget you want to modify.

HTH