GhostWire Button [fitLabel]
The fitLabel property of the Button component can be switched on/off from the Properties Panel.

false
If the property is set to 'false', the button will stay at its size regardless of the length of the Label. Not recommended, because your text gets cut off (technically speaking, the Label is masked off).

true
This property is 'true' by default, meaning that the button will resize itself to fit the length of the Label you have specified either during authoring or runtime.

live preview
Due to the live preview, you would see the button on the Stage to stretch as you change the Label property to a longer string.

Note however, a Live Preview doesn't resize your button on the Stage - only when the movie runs would the resizing occur. Therefore, if you try to select the button on the Stage and nothing is happening, you may actually be clicking outside the button - you may for example, be clicking to the far right of the button.

To fix this issue, you should resize the button on the Stage using the Free Transform Tool (Q). The Live Preview will help you see what you will get when the movie is published, but to make authoring easier, you should resize the button. It makes no difference either way when the movie is published, but selecting your components during authoring will be easier.