How can i stop my 20month old chucking tantrums if she doesnt get what she wants ?

Your daughter is seeking attention whether with good or bad behaviour. My grandson is also at this stage and screams when someone else has a toy he wants, or even his toy. Been my experience and advice from others is to try to ignore the bad behaviour - the child wants a response, the child is used to u giving in, understandably for a peaceful life. Rewards good behaviour and try ur best to ignore tantrums etc. Wish u well