Greetings, Lysandra! I adore the double family idea for traveling on vacation. What fun for you and your daughter! There are plenty of peaceful rides that your friend's baby can enjoy, and I’ll be glad to share them here!
Of course, rollercoasters are off the table, but rides like
Peter Pan’s Flight, Small World, and The Country Bear Jamboree are pleasant to experience. There are no jarring noises or surprises, other than the magical sights you will see! Open air attractions, like Dumbo, the Flying Elephant, Aladdin’s Magic Carpet Ride, and People Mover are great options in Magic Kingdom.
In Epcot, you may enjoy the World Showcase and the
Gran Fiesta Tour boat ride in Mexico, as well as using
Rider Switch to enjoy Soarin’. It will easily leave Mom in a peaceful and inspirational mood that baby will pick up on when she returns! Disney’s Hollywood Studios doesn’t have too many rides without loud noises or simulators, but they may enjoy watching the Live Beauty and the Beast Show, with colorful character and songs everyone will recognize. It’s plenty of sweet magic, right onstage in front of you!
There are a few attractions with loud noises, such as Pirates of the Caribbean with it’s cannon fire. Haunted Mansion does have a few scary pop-ups, and the Enchanted Tiki Room’s Tiki Gods may be a little overwhelming for someone with sensitivities. If you’re ever in doubt about an attraction, there is always a Cast Member at the head of the ride that can give recommendations about what's inside. Please let me know if I can help any further with your magical vacation! ~ Lindsey P.