Thanks for the added info. Since you say that the droppings are mostly water, then this is likely an increase in urine (polyuria). There are many causes for this and can include, but aren't limited to, reproductive activity, renal disease, malnutrition, toxin exposure, and diabetes.
Cockatiels are the birds that we can commonly see egg laying in, even without having a male around. Often before they produce an egg, they will have a change in the droppings -it becomes larger and more wet. So, please watch her over the next couple of days as if she is going to lay an egg it will be soon. Please watch her for any signs of pushing, straining, breathing changes or being down at the bottom of the cage. If you see anything abnormal, she will need to be seen by a vet ASAP.
If she is only a seed eater, then she is likely malnourished. Malnourishment can cause many health issues including renal issues. I would highly recommend that you work on her diet if needed. She should be eating primarily a pelleted diet, then healthy veggies like carrots, sweet potatoes, dark greens. Seeds would then become a smaller (10-15%) of her diet. This is obviously a long term issue to work on. Here is some information. See: http://cockatielcottage.net/finicky.htmlhttp://www.birdieboutique.com/switch.htmlhttp://www.harrisonsbirdfoods.com/
Diabetes is not the common in birds , but it is most likely to be seen in cockatiels. They often drink more and then urinate more. Please monitor her water intake over the next 24 hours. Measure the amount of water you put in her water cup, 24 hours later, measure the remaining water and calculate the difference. The difference will be the amount consumed. Obviously this won't be accurate if she takes a bath in her dish :) Please let me know what the amount consumed is.
Review her cage and he surroundings and make sure there isn't anything metal she could have chewed on. If you find anything, please save it and make a vet visit as metal toxicity is quite serious.
Diarrhea is very uncommon in birds so please do not use any over the counter product as these are generally unsafe and not effective.
So to review, observe for signs of possible impending egg laying, measure water intake, review caging, work on diet (long term). Depending on what you find out, she may need to be seen by a vet so if you don't know of one, you can search this website. There are quite a few in FL. See: http://www.aav.org/search/
I will check back tomorrow to see what you have found out about her water intake. Please let me know what other questions you have right now.