A combination of the alien design, the way the alien says this, and the fact it leads to an alien stealing Muriel's kindness, and it makes for one of the most memorable episodes in the series overall.

Source: https://comicbook.com/anime/news/courage-the-cowardly-dog-best-episodes-ranked-top-10/

The cake was a tribute to Muriel's part-time work at the newspaper, where she worked in the office alongside her husband, Philip Rees, who worked there as office manager until his retirement.

Source: https://www.expressandstar.com/news/local-hubs/staffordshire/stafford/2023/04/11/former-es-worker-muriel-making-headlines-as-she-celebrates-100th-birthday/

When it comes to Muriel's age, however, the series doesn't provide too many clues.

Source: https://screenrant.com/virgin-river-main-characters-ages/