Try to find out what the program will be. Prepare her ahead of time by telling her some story about the composer(s) life and why each piece was written. What was the style of music when it was written? How would she recognize the era in which it was written...what characteristics should she listen for? What is it about the piece that people living now (assuming it is not a currently living composer) like enough to listen to it? What do you like about the piece?
What does she hear in a piece of rock music that she likes...what causes her to like a particular piece?
Engage her by finding out what characteristics appeal to her in the music she really likes. Melody? Drama? Lively beat? Chord progression? Lyrics?
Knowing what she likes to hear will give you a way of explaining what is going on in the piece.
Some time ago, as a naive listener, I found that listening to a chamber group playing was more accessible than a full orchestra.
When you listen to a really good chamber group, you can imagine a group of friends sitting in the parlor (or bar!) having a conversation. There isn't as much to take in all at once as there often is in orchestral pieces. In a way, for a naive listener, it isn't as overwhelming a musical experience, and is much more intimate.
You can focus on the individual musicians and how they interact with each other through the music.
It should lead to an interesting dinner conversation later.
When the sun shines, bask.
Classical Guitar forever!