Hello Emily,
Welcome to planDisney! Traveling to Walt Disney World with a toddler is such a magical experience. They probably won't remember the trip at all, but you will get to experience everything through their eyes, and the view is amazing! You are sure to make some priceless memories.
As wonderful as everything can be at that age, there are a lot of attractions that can frighten small children. It's great to see that you are preparing yourself ahead of time. As far as "small drops," the first attraction that comes to mind is
Pirates of the Caribbean. I that ride you might compare the small drop to being at a playground and going down one of the smaller slides. You definitely feel the drop, but there are no seatbelts or lap bars because it's fairly gentle, just a little surprising.
Frozen Ever After in EPCOT has two similar drops. The first one goes backwards and the second goes forwards. Again, the boats on this ride don't have lap bars or safety restraints. While the drops do add an element of surprise, they are fairly gentle.
Another "drop" I've heard guests mention is on
Peter Pan's Flight. This attraction runs on a skyliner-type track, so you are suspended, and there is a moment where you go from a higher level to a lower level, but it's fairly smooth.
While most attractions without
height requirements are gentle, motion-wise, some rides can be a bit scary for young children.
Haunted Mansion is one obvious choice, but Pirates of the Caribbean may also be a bit too dark for your little one. It's
Tough to Be a Bug in Disney's Animal Kingdom is another attraction that has some intense moments. You know your little one best, so you'll know what she'll be eager to ride and what you may want to save for another trip.
Hope this helps. Have a magical vacation!
Diane