... as Microsoft has made Windows a dead end with the Windows 8 fiasco.
If all she really needs is email and a browser, look for the simplest, cleanest UI you can find that provides that very basic functionality. Then configure the UI to looks like what she is used to - Windows XP.
Don't over complicate the transition with things you might think are cool, just keep it complicated enough to meet her needs, no more.
"Any intelligent fool can make things bigger and more complex... It takes a touch of genius --- and a lot of courage to move in the opposite direction."