If you wish to get over your fear then try spending a little more time with your niece.
Spending time together will help you grow more comfortable around her, get to know her better and find out the things that make her tick.
I have a two year old son and I find that most of the time all kids want to do is play. So, find out what she is into and then play with her.
Kids just need attention, they don’t need lots of money to be spent on them or lots of flash toys. They just crave your time and affection.
Hope this helps a little, you will be great 😁👍