What should i do if my daughter had started refusing to go to school after an embarring incident?

my daughter, willow, had been very attached to me since birth and is a very shy girl. she always cries and expects me to do all the talking for her. she had started school, but doesn`t like going. she does not feel at home there and is not comfortable to be around so many children she doesn`t know. she had recently done a big poo on her seat. the teacher was singing to the cl and willow did not want to interrupt. she thought she could hold it in until recess, but it just came out against her will. she felt really humiliated. the other children thought it was disgusting and teased her about it, which made her feel really ashamed. she tells me that she will not go to school anymore and will just stay at home with me where she feels safe and secure. even joel, her older brother, made fun of her and told her that she must be even lazier than her bum. he tells her what all the names the other kids will call her and that made going to school even more fearful for my shy, insecure daughter. how can i make things better for her?