Another scene from an older black & white movie. This is from a bigger-budget feature film of 1939, she is using an early 'twenties Remington Portable.
As she inspects the machine and then goes on to type a note on it, she still is not really smiling.
How can you be using a clean and crisp little Remington Portable and not have a smile on your face. She definitely is acting, must be.
As proof that she can smile, even laugh - later in this film she does actually laugh. (At the time that was noted as quite an event of itself.)