One of the things I like about forums is that you can ask one question and you get a variety of answers, from "I don't know" to snarky comments to jokes to bare bones "yes" or "no" to informed answers. The best answers are those that provide information. Then you can make up your own mind which may or may not agree with the conclusion the responder came to.

I treat doctors the same way. Their job is to provide me with information, not answers. I take their information and come to my own decision.

Some doctors respond to this approach more favorably than others. Residents and new doctors respond the best. They are used to being beat down and questioned. They like me because I'm not trying to convince them of anything, I just want information.

This is my long winded way of saying that I find it not only acceptable, but recommended, to seek information from multiple doctors, especially when one doctor gives you an answer that doesn't seem right. At the very least I'd want to know why she thinks you shouldn't bike. Maybe she knew someone who lost a pregnancy due to a bad bike wreck and it left her scared. That doesn't mean the same thing would happen to you, an accomplished (I presume?) cyclist.