My sympathies, we haven't lost one like this, so can only offer general points.
I can't see anything you could have done - she was getting up and drinking, so like you I would have said - ill pig but no great concern, leave 24 hours and expect her to get better.
My only thought would be about the potatoes - were these cooked or raw? Green potatoes are poisenous in larger quantities to pigs (one or two will just make them feel off). I gather this is due to an alkaloid, called solanine. This develops in potatoes when they are stored in the presence of light (which also encourages chlorophyll formation giving green hue).
My other thought is whether something is starting to grow, or come into flower in the area at this time of year. Have you had pigs on here for more than a year (so have seen the full cycle of plant life)?
Obviuosly keep an eye on the others, but if no-one else shows signs, then hopefully this is a one off.
You could get her PM'd, but this would be very expensive, and probably be inconclusive. However if a second one succumbed, I would PM it immediately.