I think what is best for the child (needs, not wants) should override what other the child or the caregivers want.You misunderstood. You are the parent and want your daughter to have anabortion because carrying the baby to term will have severe and life threatening consequences. You are a parent and want your daughter to undergo cancer therapy because not doing so will result in a substantial likelihood of her death.
Should her opinion carry the day at 11 years of age? Or do you have a right to intervene? Parents and guardians have the right to make medical decisions for their child. This is true over the child's choices to a point. The parent enjoys a legal presumption that they are acting in the child's best interests. This can however be challenged and the presumption can be overcome. The same is not true for a 45 year old woman. That is because a child does not have the same rights as an adult.