Before placing blame on your granddaughter ONLY and for all the expectation to fall on her to make a change (that she may not have a physiological ability to do so), I would recommend an approach to understand which particular noises cause your granddaughter distress and have all family members contribute to adjusting their behavior to not cause such annoyances. It will help create a more harmonious environment for everyone. Family is teamwork and everyone needs to be ready to compromise.

If one having misophonia may seem like an inconvenience to others, the same goes if one is dealing with family members or friends with Autism. People must be open to making adjustments to their own behavior as well. I personally have never met one person who doesn't have an issue with something.
Family therapy is extremely important, and I hope that you and the rest of your family members will support each other, rather than conclude that your granddaughter needs to receive drug treatments and hospitalization.