When she was seventeen, Niamh took Ciara's big stallion, Embarr, out for a ride one day and, as she has never been particularly good with horses, she promptly fell off his back and broke her leg. As the quality of medical care on the island of Viridis is rather primitive, even for a quasi-medieval society, Niamh's leg was not properly set and it healed badly. It took a long time for her to heal and to get to where she was able to walk without too much pain, but her leg has troubled her ever since. Most of the time, she is able to ignore the twinges and slight stiffness in her leg and live her life as she pleases. But even now, more than a decade after the accident, there are days when Niamh has trouble walking. She is too proud to admit it of course, but fortunately for her, Ciara can usually tell and she knows that Niamh is grateful for her help during those times.
Interesting fact: This is how I'd originally imagined that the girls might look. Largely, in Niamh's case, thanks to Ciara's habit of sneaking her chocolates while her leg healed.
