My 4 year old is having self image issues: Advice?

My daughter is in preschool. And since she has started these last 2 weeks or so she has been saying she isn’t beautiful and that kids say it to her, which is crazy cause they are only 4 years old! And she is such a beautiful girl. We have people always telling us how beautiful she is. Why is she only 4 years old having self image issues already?! What should I do?I told her to tell her teachers who is saying it to her and if they don’t do anything momma will talk to the teachers so we can figure it out. Any advice please? (No harsh comments.)