I completely respect your right to do this...but do you honestly think your daughter doesn't hear "objectionable" songs? Either by listening to a friend's ipod, or the radio, or in the car going to the movies (if you aren't driving) Or maybe your point is not that she can't hear it, but you don't want to support the music by allowing her to buy it?
I have been known to change the radio station in the car when I do not like the lyrics, but I will discuss with my dd why I don't think it's appropriate.
We try very hard not to spend discretionary money on things we don't want to support. Lady Gaga would be one of those things, as would many misogynistic rap "singers."
I know my dd hears things I don't like--she wouldn't be asking for those songs if she hadn't heard them somewhere. But she's not listening to them endlessly, either.