Well, if she doesn't like country, I wouldn't put a ton of it in...if you are doing this as a gift for her, think about what kind of music SHE likes. You didn't say what kind of music she likes!
I love oldies, so that's what I would use if I was making one for ME. Songs like "Little Darlin," "Let the Little Girl Dance," "Remember When," etc, I think would work for a slideshow with little ones.
Or if she enjoyed music during the 70s, some good ones I might us are "Hello Old Friend" by Eric Clapton and "Dream Weaver" by Gary Wright. Both of those songs move me when I hear them!!
And if you want a truly great (sort of) country song, I'll tell you my favorite...from the 70s, I believe, called "I Believe in You" by Don Williams. Maybe if you YouTube it, it will be there (haven't checked) but it is SUCH a beautiful song, with beautiful lyrics!!! Check it out, just for your own enjoyment, at least.