Are you a doctor? Not being rude - seriously. You don't know her medical history. Perhaps the OB is just conservative or perhaps there's more going on? Either way, if I trusted my doctor and they told me not to go, I wouldn't.
And for the record, I went do WDW multiple times while pregnant - because my doctor gave me the green light. And when she told me NOT to take a trip, I didn't. Different strokes for different folks, I guess.