At 3 year old studies can have less rules I would think, and maybe some laxity of time ,at home when she wants everything immediatly ignore it ,if she yells thats okay, if you give way she has won the battle, the answer is to comply if you can with what she wants, but if you are busy at that moment tell her,'I will help you shortly' if she yells simply say nothing , when she is quiet you then consider if you are ready to do what she wanted ...be consistant she will get ther message and wait .Good Luck