Young Sibling acting like baby ?

Question for young mamas who still live with their parents.

So I’m, 19 , 30 weeks +2 days pregnant, and currently living with my parents (moving out in December once I’ve fully established my credit)

I’ve noticed that since I’ve been pregnant my little sister who is 9 has been behaving like a baby. Carrying a bottle full of milk around and drinking it, has a pacifier from wherever and a blanket calling it a “blankie” she normally does not act like this.

She also tells my mother that my mother won’t love her anymore once my daughter is born.

Is this normal for a younger child to act/behave this way when a new family member is coming in?

And do you have experience with it? Just curious.

Also what can i do to make her feel more included with the baby instead of letting her linger to act like this. I was thinking maybe a present for being an aunt?