If she has any warning signs such as cough, breathlessness, any grunting sound while breathing, colicky abdominal pain, you should take her to the ER. Gradually increasing pain is also an indication. Otherwise you may observe for a day. Mostly likely the pain will resolve by it on in a day.
The pain below sternum can be due to a musculoskeletal cause (as in from the muscles and bones of the rib cage), an intra abdominal origin or a pleuritic (lung) origin. Most of the times this symptom is bit specific (not suggestive of a single diagnosis). Watch for the alarm signs mentioned above. Avoid Ibuprofen and pain medications, as it can aggravate the pain, if the pain intra abdominal origin as in case of gastritis.
Hope this helps
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