I'm assuming this is a live rat?
I would say get a little 10 gal tank or critter keeper and all the supplies for keeping a rat for a while.
Ball Pythons can be very picky eaters and sometimes will go on fasts. Your snake will most likely not eat EVERY time you offer it a meal. This will happen again.
Just offer it again when the next feeding day comes around.
Dont try and offer it to the snake too often, this can "turn the snake off" and stress it.
Dont worry she can go without food for a long period of time, just offer it to her in a few days and see what happens.

You can always convert her to frozen/thawed, then you dont have to go buy a live rat every week, you dont have to keep the live rat if she doesnt eat it. And you prevent your snake from sustaining fatal injuries from rodent bites.

Another thing is did you change anything around in the cage in between when she ate and now?
I find that if I just did a cage cleaning, or moved hides some of my snakes will be to busy exploring their cage than to eat that day.