It is weird, but actually the subject is "la pizza". "le" is an Indirect Object. In Spanish Indirect Objects can be identified as "me, te, se, le" pronouns most of the times and, unlike Direct objects, they refer to people. In this sentence, "le" and "a mi novia" are exactly the same. It could sound redundant, but actually this repetition is very common to emphasize the idea that she doesn't like pizza. This is called "dativo de interés".
I hope this is not more confusing.