She is an SPA or Single Page Application. To help you understand, imagine that an SPA is like the human body. Depending on the time of day or the event you need to attend, you change your clothes accordingly but your body still remains the same.
Client-side routing works the exact same way: Your app itself is the human body. The components in the app are the clothes that change depending on what URL you’ve requested.
Test out React Router and the smooth navigation client-side rendering has to offer with Sally.