sometimes children her age will wear little pink skirts which you can buy at farmers stores but sometimes the ballet teacher will have her own collection.
she may need a pink headband to keep her hair out of her eyes.
she might also need a crossover top that you can buy at ballet stores incasre it gets cold and if she is doing character work she will need a character skirt and shoes which the teacher usually has too

aside from what you’ve mentioned (shoes, etc.) she may be allowed to wear a ballet sweater in the winter, maybe a leo with an attached skirt, be sure to ask her teacher if there’s a dress code. also, make sure you can secure her hair away from her face.

Other than those three items, everything else is optional, such as a dance sweater or a little dance skirt … but since she is only three, I would not recommend either one. At that age, they tend to get very distracted with clothing articles that are easily removable.

A leotard with an attached skirt is usually very popular with young ones.

Seems like they would have told you. I think you have it covered. I want to commend you for enrolling her. Even if she does not become a ballerina, she will learn immensely and it will help her the rest of her life. Don’t make it a competitive thing though, and if it is not her thing, it is not.
I hope she loves it.
And good for you for giving her opportunities when she is young.