There is little or nothing she can do. The existence of the right of way was specifically brought to her attention when she bought, and this is quite enough to oblige her to respect the right of way. The exact scope of the right of way might be open to debate (is it on foot? is it vehicular? is it for a specific purpose? ) but the time to investigate and get answers to these questions was when she bought.
Incidentally, a right of way would not usually include a right to park, so if the neighbour is parking on her driveway, she would probably have good grounds to object to this.