Hi,
Congratulations on still being able to do this as many of use are having issues with this.
However at her end she need to open System Preferences > Sound > Input and check the volume is not set to high.
This will cause the Mic gain to bounce the graphics into the right hand end and some "clipping" will occur. (it cuts the sound to "protect" the system)
The Mic should be selected here.
It should also be selected in the app in Preferences > Video and Audio Pan and then the Microphone Drop down.
In some cases it should be done in that order (System Preferences then App).
If it is an external Mic then either it should be moved further away or the Volume in the Input pane should be reduced further.
Possibly if she happens to use a Firewire or USB based Midi Audio sound system then that might add complications.
Check Applications/Utilities and the Audio MIDI Set up.
This can add further "gain" to the Mic used which might be causing distortion.
Is there any chance she ia actually using a Distortion Add-on ?
SoundFlower can add functions to the Sound set up and might responsible https://rogueamoeba.com/freebies/soundflower/
There are others.
9:02 pm Sunday; January 31, 2016
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad