Well, it shouldn't be terribly difficult to get things going. I guess the first important question to ask is if the remote in use on her TV is the one that came with the set. If it's an aftermarket universal, then it may not have the button or code you need.
Second, the switch you've described at the top of the remote wouldn't switch inputs on the set. The remote you've described can control more than just the TV. The switch at the top tells the remote what device you want it to talk to.
Sony uses the term TV/VIDEO to describe changing inputs. There are other common terms though. Look for a button labled "INPUT" or "AUX" or just "INP". On other sets, sometimes you have to channel down below Channel 2 (or higher than the largest programed channel number), and your Aux inputs reside there. There could be other ways or buttons. Give a look. And if you want, list some of the buttons the remote has. Maybe I could tell you which it is.
Very important question: Is it the original remote?