Costochondritis: This is a common condition characterized by inflammation of the cartilage that connects the ribs to the breastbone. It is often seen in young women and can be exacerbated by deep breathing or movement. The use of birth control may also contribute to increased risk of costochondritis due to hormonal changes.

Musculoskeletal strain: Given the patient's age and the absence of injury, musculoskeletal strain from overuse or poor posture could be a contributing factor to her rib pain.
Precordial catch syndrome: This condition is characterized by sharp, stabbing pains in the chest or rib area, often precipitated by deep breathing. It is more common in young adults and can be recurrent.
Gastroesophageal reflux disease (GERD): Although not directly related to rib pain, GERD can cause chest pain that may radiate to the ribs, especially with deep inspiration, due to acid reflux irritating the esophagus.

Pulmonary embolism: Although less likely in a young, otherwise healthy female, pulmonary embolism is a life-threatening condition that must be considered, especially if the patient has risk factors such as recent travel, immobilization, or a family history of clotting disorders. The use of birth control can increase the risk of thromboembolic events.
Pneumothorax: Spontaneous pneumothorax can occur without trauma, especially in tall, thin individuals. It would cause sudden onset of sharp chest pain that worsens with deep breathing.
Cardiac conditions (e.g., pericarditis, myocardial infarction): While rare in young women, cardiac causes of chest pain must be considered, especially if accompanied by other symptoms like palpitations, shortness of breath, or radiation of pain to the arm, neck, or jaw.

Tietze's syndrome: Similar to costochondritis but involves inflammation of the cartilages and surrounding tissues of the ribs. It is less common and can be distinguished by the presence of swelling over the affected area.
Sickle cell crisis: In patients with sickle cell disease, a crisis can cause severe pain, including chest and rib pain, due to vaso-occlusion.
Osteoporotic rib fracture: Although rare in a young female without significant risk factors for osteoporosis, it could be considered if the patient has a history of minimal trauma or has risk factors for bone disease.