She is worried about their future.
That’s why she hugs him.
The equation on the right is the continuity equation for electrons.
This equation enforces charge conservation for the electrons.
A continuity equation is somehow a form of conservation law.
It other words it states that some properties of a system do not change as the system evolves over time.
When she hugs him, she hopes that her feelings are not going to change over time.
But the equation is defined for electrons, not for humans.
So his arms do not fully embrace her.