My girlfriend doesn't really like musicals like I do -- she does have a passing interest, but nowhere near mine. It's not a big deal between us. There's plenty of other things we agree on and talk about.
If you really feel this is a big deal, though, find out what kind of music she does like, and find musicals in that genre to pique her interest. Then see what happens from there. But don't force musicals on her. Actually, don't force anything on her. If she doesn't like 'em, she doesn't like 'em. But I don't see why non-love of musicals should be a dealbreaker.
"You mean what was the best picture of the year or what did they pick as the best picture of the year?" - California Suite