Before Irene could go on a journey far larger than she was, but undoubtedly possible based on her father's explanation, which lasted well into the night, there was one last thing she needed to do before she could pack up and leave.
Supplies weren't an issue. She was accustomed to setting up camps in unsavory places. Even sleeping in the winter was something she had learned well in the war—many travelers often said that they could warm themselves up better when it was just them all alone rather than having to share a fire with an entire army of men.
What was the issue was that Sorrel was growing older and, while he was fine for a few days at a time, she had been noticing the grey hairs that popped up throughout his mane and body. If she wasn't mistaken, he was a bit harder to rouse in the colder weather as well.