Well, let's see...
Country music is popular in the Southern part of America, and most of the singers are from Southern states (Texas, Oklahoma, etc.). Everyone knows that we Southerners have certain words all our own which get incorporated into songs, such as the ever-popular "y'all", "Howdy", and "fixin'". Some Southerners have an accent depending on what part of the South they come from. This does not cause them to botch the English language in their songs, however. Everyone who hears country understands the words that they hear.
Now, let's look at rap. Rapping is talking -- talking, not singing -- very very quickly, to music. This talk is often riddled with cursewords and slang. So if you can make out something the first time, you probably won't like what you hear. You may also not be able to comprehend what the "singers" are saying because of all that slang.
IMNSHO: Country is far better.
Tell her that the country-n-western music scene has far more class than Rap/Hip-Hop.