Step1
Find out why he likes this music so much. The first phase of your plan is to get into the psychology of why someone would listen to terrible music. Some people have an emotional attachment to certain types of music because they relate it to a certain time in their lives. Perhaps her father listened to country-crossover and she has positive memories attached to those times, so now she listens to country-crossover. Perhaps in college, an early girlfriend listened to adult-contemporary so now listening to adult-contemporary reminds him of those positive times. Showing an interest in why she listens to what she listens to will make her trust you because you're showing respect for the type of music she likes. This will make it easier for you to begin phase two of the music take-over plan.
Step2
Talk about artists you like that have something, anything, in common with the artists she likes. At first, it can even be a bit of a stretch, but finding some common ground on which to begin to talk about bands or artists that you like to listen to is your audio foot in the door. Say, again, she listens to crossover-country, and your friend is playing one of her songs. You can start a conversation such as, "That slide guitar reminds me of a track on Wilco's 'Being There' album." This will, most likely, be the first time in a long time that you or anyone else has expressed interest in her music. She will most likely want to engage you in conversation but, remember, you have the leverage, here. You're the one that initiated the conversation, so keep control. Constantly bring the talk back to YOUR band. This leads us into phase three.
Step3
Entice your friend with the good music that you listen to that has things in common with her music. Once you've initiated a conversation about a band, or artist, that has something in common with the music she likes, really play up the similarities in the music style. Do this in a way, however, that makes your music sound "humbly superior" to hers. "Wow, Kathy. I didn't know you liked reggaeton. This guy's all right. He sounds like he's been listening to Jurassic 5, the way he's spitting his rhymes." This will make her think, "Gee, he's not making fun of my music, AND he's talking about a band that reminds him of the music I listen to. I bet that band he's talking about is pretty good!" This brings us into the most important phase of the music take-over plan.
Step4
Make a mix for your friend. This is a delicate and complicated art. Not because making a mix is difficult, but because this particular mix must be programmed specifically to trick your friend into listening to good music. Start the mix with a song by an artist that she likes. This will most likely be a song you hate. Follow that song up by another, less obnoxious song by another artist she likes. Then, on the third song, slip in a song by the band you were discussing. Then go back to a song by one of her bands. Then, on the fifth song, slip in a song by a band you never mentioned, but is similar to the band you were discussing. The next song is tricky. If you can, find a song she hates by a band she likes and make it the sixth song. Then, follow that up by another song by a band that is similar to the first two bands you mentioned, but takes the sound even further away from the type of music she likes. This will make her think "Wow, I liked that song by this band that I've never heard of MUCH more than the song by the band I like!" After this, finish out the mix with only songs by new artists she's never heard of.
Step5
Invite your friend to see a band you like, live. There's nothing like a live show to secure fan-hood. Once you've made the mix and planted the seed, find out which band she liked the most. Treat her, then, to free tickets to see them live. Once she likes the music at home, she'll love the music live, and you'll have a convert, 100 percent.
Novice 
