Yes, you need to be connected to the same local network as the Roku - cellular data can't work for this.
I'm not familiar with RoByte, so I'm kind of grasping at straws here.
Similar inability to locate Roku devices has been reported lately by people using the iOS (Apple) version of the official Roku remote app. Might you be using an Apple phone as well?
Some routers can be configured to let individual clients connect to the internet but still not interact with other devices on the same network. Might your sister's router be set up this way?
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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