As Lightfoot has said the path to the settings for subtitles on your TV can be found by pressing the Home button on the Sony TV remote control.
From there scroll downwards to Settings.
Select System Settings.
On the next page scroll down to Channel Set Up.
Click right and select Digital Set Up.
Now select Subtitle Setup.
Click on Subtitle Setting and select either Basic or For Hard Of Hearing.
Also make sure that the Primary and Secondary Preferred Language options are selected for the languages(s) you prefer.
Now press the Home button to come out of the Settings menu.
Subtitles should now be permanently displayed on the TV.
Please note though that not all Channels and programmes carry subtitles, so no amount of going through Settings will bring them up. Perhaps you could explain that to your mother so she is not tempted to press random buttons in an effort to get subtitles when they are not available for a particular programme or channel.
There is a button on the Sony remote control which can switch on or off the subtitles.
This button is located on the bottom third of the Sony remote control, it is located in between the Audio and Title List buttons.
It is a small square with four dots at the bottom.
Pressing this button will bring up a submenu Subtitle Language where you can switch off the subtitles by selecting Off, to switch them back on you would select English (assuming English was chosen as your preferred language.)
As the Sony TV remote controls so many functions on the TV you may want to hide it from your mother so she is not tempted to go on a button pressing frenzy which can only add to confusion and getting lost in the many options available.
Once you have got the TV set up to display subtitles permanently as described and you feel the dementia remote control offers the basic functions your mother needs, power on/ off, channel changes and volume control, you can maybe take the Sony TV remote away from temptation.
