First off you will need to know if its onboard sound or if she has a soundcard easiest way is just to look at the back of the pc if you see something like this at the back then its on board:
http://www.overclockersonline.net/im...6362/ports.jpg
if its in one of the lower slots so it`ll look like this, see those metal plates at the bottom 7 in total and 1 is missing right. Well if the sound holes are there its a soundcard and not onboard.:
http://www.amtrade.com/case/774_tool...rcase_rear.gif
I think its probably onboard though, so you will need to find out the motherboard manufacturer and number it appears on bootup normally. Could be one of the following ASUS,ECS,BIOSTAR,INTEL,GIGABYTE,MSI,ASROCK,FOXCONN ,ABIT
it will also have some numbers after it so try to note it down. This can be difficult to find so note anything down you can its normally the first screen as soon as you turn on the pc it has all the info.
If you struggle to do that try downloading this software called everest you can find a link below in my sig. Once installed click computer then the motherboard section in there it will have hopefully all the information you need.
Once you do find out your motherboard make you can just google it and go to their website, you can then find the drivers you need to download and install.