Hah! Although I thought it was a Zenith, I was wrong. I found the exact model remote she had. It was an Admiral. When I learned that Zenith used tuning forks, not whistles, I began to doubt myself. I’m pleased to see I’m not going crazy. (Or, at least, that this is not evidence of it.)
https://www.worthpoint.com/worthopedia/vintage-1960s-magnavox-phantom-tv-455118231