Final answer:
The likely diagnosis is vitamin B12 deficiency.
Step-by-step explanation:
The likely diagnosis for the 24-year-old woman is vitamin B12 deficiency. The symptoms of fatigue, numbness, and tingling in her feet, along with the low B12 level and high parietal cell antibodies, are indicative of this condition. Hashimoto's thyroiditis and autoimmune adrenal insufficiency are unrelated to her symptoms and lab values.