言ってる is an informal and colloquial version of 言っている, and it sounds fairly out-of-place if used in a solemn narrative part of a novel. So let's compare the following two phrases instead:
言っている can only refer to something that has already been said, so when this phrase refers to something yet to be said (i.e., "as if she is going to say"), 言うかのように is the only option. In your case, however, the two phrases are interchangeable because they refer to something that was just said. Maybe 言うかのように might sound slightly more literary (don't ask me why), but the difference is minimal.