Strokes are actually quite common in pet birds. We think that atherosclerosis secondary to fatty diets should be incriminated but other nutritional imbalances may play a part as well such as a calicum deficiency. Your parrolet will benefit from being attended to by an avian vet (please see here: www.aav.org) who is likely to administer diazepam (Valium) and calcium by injection. Supplemental oxygen therapy should be considered as well. For now, please heat her environment up to 85F, remove her perches and place her food and water on the bottom of her cage along with her.
Add a water soluble avian vitamin such as Oasis brand to her water at half of the recommended dose so as not to make her water distasteful. Add a calcium supplement such as Calcivet or Calciboost to her water. These supplements are available in pet/feed stores. Avoid over the counter antibiotics designed to be placed in her water. They won't be effective if only because an ill bird won't drink enough to medicate itself properly.
Nutritional imbalances are a common cause of illness in our pet birds. What has her diet consisted of, please? Seeds should compose less than 20% of her diet. Ideally, a balanced pelleted diet such as can be found here: www.harrisonsbirdfoods.com or here: www.lafeber.com/pet-birds should be fed as well as hard boiled egg yolk, pancakes and cornbread, the tops of fresh greens, dairy products such as yogurt and cheese, fresh fruits such as apples, pears, melon, kiwi, and berries, vegetables such as broccoli, carrots, beets, asparagus, cabbage, sweet potato, and squash, and even tiny pieces of meat.
Please respond with further questions or concerns if you wish.