my cousins a brat

currently 31 weeks pregnant and i have a 5 year old cousin (my parents had me when they were 22 and my uncle and his wife decided to have kids in their 40's) tonight while we were at dinner at my grandparents house my cousin came up to my while i was sitting on the floor and kicked my belly, she said she was upset because the baby got more gifts then she did (she's always like this, she's very spoiled and not disciplined at all and when she does stuff like this her parents don't say anything) obviously i was very upset and in pain, and i said a few things and my aunt and uncle got upset because of the way i was speaking to her...i told them she will not be aloud to hold my daughter because she's aggressive and doesn't listen, when she's told no she just does it more and laughs and pretends it's funny....am i over reacting by telling my aunt and uncle she won't be aloud to hold my daughter until she starts behaving? she picks things up that are fragile and when told to put it down she throws it and breaks it, and i'm just worried she's gonna toss my child or hurt her (obviously we wouldn't leave her unsupervised but still) please help 🙃🙃🙃🙃