4 years apart you will be fine. Nothing to worry about

""this is your sister, love your sister, protect and take care of her, we love you both".

bound to be a little. Your daughter is soon to have her personal space and time with you irrevocably changed !
Probably best to say that your daughter is the big sister and that means having to learn to be patient. Also that her brother/sister needs them to show them how things work.
Daddy needs her to help him look after you. You should say the same about daddy.

Tell her to repeat this over and over: "this is my sister. There are many like it but this one is mine. Without my sister, I am useless. Without me, my sister is useless."

I think a lot will depend on if she has a sister or a brother. I remember my brother being such a pest but we bonded well as we grew older. Eventually he became my protector.

my 2 oldest daughters are exactly a year apart and complete opposites

Well congrats but it's too early to assume there will be sibling rivalry

I got along well with my sister's and brother

involve her in every thing so she still feels she is not ignored

Sometimes they get kinda protective

Relegate d older one to d garage

We were lucky never really had it with ours - older boy and 5 years difference. Due to the age gap I'd expect it to be less of a problem than I've seen in my extended family when the siblings are closer together in age

just try to keep her involved with the baby too......but still make sure she has her "own" time with you and Dad too.......it will be fine.

Include the older child,plus spend time alone with her too. Take her out,play games with her etc

My daughter once asked if we could take her brother back to the hospital and trade him in on one that didn't cry

besides don't show favoritism. It's going to happen anyways

Always make time for each kid

Have a son?