Looks like you have parts from the following sets:
- Hat and maybe a shoe from Tea Party
- Hat from Best of the West
- Pony skirt from Megan and Sundance Picnic in the Park
- Pony skirt from Megan and Sundance Country Jamboree
- Tutu from Mommy and Baby Ballerina set
- Skates and saddle blanket from Great Skates
- Cape and crown (x2) from Pony Royal
- Nightgown and cap from Sweet Dreams
- Dress and shoes from Party Time
- Shirt, skirt, pom pom and possibly shoes from Pom Pom Pony
- Baby shoes from Pony Workout
- Ice skate from Snow Angels (I think? It's kind of covered up)
- Dress from Sidewalk Surfer
- Dress and shoes from Get into the Groove