Show preferred resolution or switch to HD automatically

My Mother lives in a senior living facility and all the residents have the same xfinity package, its non x1 service, and she has a RNG110 cable box. She is not capable of hitting the enter button (several strokes) at the prompt to switch to the HD channel, and she cant remember the HD channel numbers. SHe can remember the easy ones like the local channels, 4,5 9,11, etc.. my question is i cannot seem to find a way to default or automatically just switch to the HD channel, the menu is pretty limited and i just cant seem to find a solution. I have programed the HD channels in her favorites and she can cycle through that way, but her memory is pretty bad and she never remembers to use the favorites button. So she has this nice HD TV and really never can take advantage, and on big TV's SD looks terrible. does anyone have an ideas?

Thanks.