Sadness is a response to loss.
Zita has lost "the gateway"—whatever that red button device is—and now she's sad.
When we're sad we lose energy, we slump, we slow down—you can see Zita doing that here.
In real life, that sadness slow-down isn't a bad thing: we need to slow down to understand the new reality we are in, without the person or thing we cared about.
So, all things being equal, we'd expect Zita to sit there glumly for a while thinking about the future she's lost—whatever that device represented to her—and then start to make alternative plans.