I went for MInt Sarah, now updated to Mint Serena. Very good for beginners, like me. Check whether you need a 32 or 64 bit version. There are loads of distros to chose from though. Take your pick really.
Here's the latest Mint downloads ( I went for the MATE version and am very happy with...
Download it onto a disc on your wife's computer.
Go into bios in your computer and set it to boot from disc drive. Stick in the disc and away you go.
It's all covered in that other thread.
Yes, Linux is free to download. You can download it onto a disc and boot it from there 'as live' to try it first even before deciding whether to install it or not. Have a look through this thread:
http://www.northstandchat.com/showthread.php?343425-Linux-and-SSD-help-please&highlight=linux...