Four year old sister at delivery?

Al
Hi, mama friends!
I am due Nov 12th with our first child (a girl). 
We are using a birthing center and hubby and I have decided that we want as few people there as possible- myself, my husband, and my mother. 
I have a four year old little sister. My mom works on the weekends, and stays home during the week with her, so there's no option for her just to "go to the sitters". So, really, if I go into labor while my step-dad is at work, my little sister would have to come with my mom. 
I've heard that children can be great comforters during childbirth, and I'm sure it would be a great experience for her. I'm just not sure how I feel about it. 
What do you ladies think? 
Should we try to arrange something for her or will she be okay?