As your 3-4 year old kid is developing, she is also able to express her emotions and have mood swings as well.
What you need to know
At this stage, your little one might throw many tantrums when she does not like something. But all this is normal as an adult too you have changes in your moods and emotions. Do not ignore your kid when she is throwing tantrums and is in a bad mood. Do not shout at her to make her understand that what she thinks is wrong. Just simply give her some time to relax and then try to understand her thought process as well.