How do I get music from my moms iTunes to my iPhone

Using iPhone, iPad, or iPod with multiple computers - http://support.apple.com/kb/HT1202 - You can manage your iPhone, iPad, or iPod with multiple computers as long as you have set the device to "Manually manage music." - E.g., adding music from a second computer to an i-device. Additional information about switching sync mode - https://discussions.apple.com/thread/4435531 and manually adding in iTunes 11 https://discussions.apple.com/thread/4597408