To me she looks like she's a little bit thin, but it doesn't look like it's at a dangerous level. She stills looks healthy. Typically you should give a ball python at least 7 days to settle in before feeding. Once she starts eating she should gain a little weight. You should probably start weighing her about once a week to make sure she starts gaining weight. I wouldn't worry about her too much unless it seems like she begins to lose weight or look unhealthy.
She's a gorgeous snake and you obviously care for her! I hope you have a wonderful experience with your new pet. Good luck!