Maximum PC

My sister's laptop [Dell Inspiron M5110] has the oddest of problems,
When you plug in headphones, both the headphones and the speakers play,
and when I go into the properties [control panel, hardware and sound, sound]
it shows the speakers and headphones under the same icon, also there was a
new device called communication headphones. Stumped, I googled the problem,
and multiple forums said to disable the communication headphones. but that has
not worked. Help?

Does it behave this way with a different set of headphones?

No yellow/red flags in Device Manager, especially the audio/sound?

No Problem Devices listed in MSINFO32 (System Information in Win7) under the Component tab?

Carefully check settings in both the audio driver and Windows sound.

I would uninstall and then install the latest audio driver. [or use the Intel auto-updater to detect and provide the real latest IDT audio driver. Note: It is possible Dell has disabled some of its bells and whistles in its driver version.]

It is possible that some wiring may be shorted not allowing the laptop to detect headphones being plugged in to disable the laptop's speakers.