Deborah,
That's true that some babies have preferences and it is fairly common, I know many women who nurse only on one side. The preference to one side may appear as early as immediately after birth or much later, even after a year of nursing. There are different reasons for this, one may be the slower flow from one breast. Baby naturally will prefer the one with a faster flow.
It could be that something triggered her and now she refused it again, babies have a good memory. In your case I would keep offering, matter-of-factly, she may go back to it again. YOu can try putting her in different position and see if this would help. Since it is only once a day, she may be able to get over it.
But, I want to be honest, there is a chance she will not get back to it. Even in this case you still can produce enough milk from one breast for her. THis would, of course, require some time for your breast to adjust to this new scenario but it is doable. Hey, I am an example that you can nurse your baby with just one breast :lol: .
Anyway, try first to be patient and keep offering, try different positions over some time, in a week you should see if it goes in good or wrong direction. If she refuses completely, let me know, I will help you, OK?