Overheating may be the cause of your problem. Using your hair dryer for more than 7-10 minutes can cause it to automatically shut off. When this happens, your mom should unplug the device and let it cool down, preferably in a cool environment for 2-3 minutes. After cooling down, the dryer can return to normal use. The reset button may need to be pushed after the dryer is plugged back in. For any other issues, the Troubleshooting Guide should be help. Conair Infiniti Pro Model 259NP Troubleshooting Guide
The first thing you should look at is the heat setting. There are two black switches on the dryer, one of which controls the heat of the air. Verify that the button is switched to the hottest setting and is not stuck on the cool setting. If the setting is on "Hot" and produces cold air, the hot/cold switch may need to be replaced. Refer to the Hot/Cold Button Replacement Guide. For any other issues, the Conair Infiniti Pro Model 259NP Troubleshooting Guide should help. Good luck!
The hair dryer might have some sort of blockage. You can start by examining the nozzle for any easily removable blockages. It could be clogged with hair or dust caught in the back grill. If that still doesn't solve your problem, it is likely that the fan of motor needs to be removed and cleaned. You can refer to the Fan Motor Assembly Guide. For any other issues, the Conair Infiniti Pro Model 259NP Troubleshooting Guide should help.