Neriah's excitement knew no bounds. But she knew she had no time. No time at all. Since by the time she reached the castle gates, the swap magic had worn out, and her face had returned back to normal, it meant Aria too was back to her normal face. It also meant by the time she made it out of the gates, Lady Bretton had realized she was dealing with a fake princess.
And knowing Lady Bretton she would have alerted the guards and her parents. So they would have been sent to get her.
Calculating the time she had and the distance she was to cover, she hailed a carriage as soon as she stepped out of the gate and told them to hurry to Gilliard port. She was supposed to walk there, but she had no time. And hailing a carriage was safer for even though she had assured Aria that she remembered the path to the port, she wasn't sure her current state of panic and fear would allow her to navigate through on her own.