How to setup liveview on a Nikon D1500?

My mom just receieved a Nikon D5100 for Christmas with Liveview. However, when she tries to use it, it says "Unable to start Liveview, please let camera cool down". What does that mean, and how does she use her Liveview?

Read the instructions that came with the camera.

I looked in the "Error Messages" section of the D5100 User's Manual (pg. 226) and found this:
"Wait for the internal circuits to cool before using live view or movie recording"

Page 105 has more information, explaining times when the Live View will be disabled to protect the camera's circuits.

Chances are, your mom had just finished doing a long video and that brought about the automatic live view shutdown.