If the budget is a concern, use what you have. If she's just getting started with this, don't immediately start throwing money at it. Once she's gotten some experience and has a workflow established, she can pick upgrades that make the biggest difference to her use case. Plus, if you wait to upgrade, the parts you need will be cheaper when you do get them.
However, if the money is there, she should consider a CPU upgrade once Ryzen comes out for better performance in Premiere. Just be sure to check benchmarks for Premiere before buying.
If it turns out she needs better gaming performance, you should get a GPU upgrade. There's plenty of info on Tom's Hardware regarding which ones are good. Just don't get more than you need if you're still new to this.