Thanks for all the replies.
I also came up with "Ain't She Sweet" by the Beatles as an option. This track used to be one of her personal favorites (though she probably hasn't heard it since 1982 or something like that). I expect it to bring a smile to her face.
I'm also thinking of using excerpts from the Wizard of Oz, to symbolize the transition from her rural hometown and Black and white photos to meeting my dad (in "technicolor"). This will pretty much be the theme for the clip. Naturally, I contemplated using cuts from Dark Side of the Moon (Breathe, Great Gig in the Sky), but they're somewhat "dark" (big surprise there, huh?).
Keep the ideas coming.