Maybe try to involve in taking care of her sister in small ways such us pick up a cloths for sister to wear or sing her favourite songs to the newborn. Make her feel important and praise her help an choices. Also give her 1on1 attention when you can, make it your special time.
I was also firstborn with bigger age gap, it was kinda strange not having all the attention but I got used pretty quickly. I find my brother to be little sh*t sometimes, but I love him to death.
Just don't stress over it, you will do great
Maybe try to involve in taking care of her sister in small ways such us pick up a cloths for sister to wear or sing her favourite songs to the newborn. Make her feel important and praise her help an choices. Also give her 1on1 attention when you can, make it your special time. I was also firstborn with bigger age gap, it was kinda strange not having all the attention but I got used pretty quickly. I find my brother to be little sh*t sometimes, but I love him to death. Just don't stress over it, you will do great