Here's are some links with general info:
http://www.healthcare.com/topic/pleurisy-during-pregnancy/
http://www.medicinenet.com/pleurisy/article.htm
Who sent her home with antibiotics--The ER or her OB/GYN? Are they sure she has a blood clot or does she simply have inflammation of lung tissue? Pregnancy pleurisy can be common, however if she actually has a blood clot in her lung, that's something else... then I'd be worried. And if it is a clot, was it from an injury or infection (e.g., bacterial infection or exposure to chemical fumes) or was it due to a blood clot somewhere else, like in her leg, that broke off and logged in her lung? How did they diagnose the blood clot, because they probably did not x-ray her while pregnant.... (perhaps its just pleurisy and not a blood clot?)
Wow... I'd involve my OB as soon as possible. Not even mentioning the risk of an embolism or stroke, I would think that just having a clot in the lung could decrease the oxygen supply available to the fetus... And low oxygen levels could also cause heart distress for her. What kind of monitoring should she be doing at home? Does she need to be referred to a pregnancy specialist?
Below is a blurb that explains how it could be a secondary effect from a clog elsewhere. Just thinking in terms of how late pregnancy blood flow interferes with circulation in the legs, if she does have a blood clot elsewhere, then her and her doctor need to know...
http://www.medicinenet.com/deep_vein_thrombosis/article.htm
A blood clot (thrombus) in the deep venous system of the leg is not dangerous in itself. The situation becomes life-threatening when a piece of the blood clot breaks off (embolus, pleural=emboli), travels downstream through the heart into the pulmonary circulation system, and becomes lodged in the lung. Diagnosis and treatment of a deep venous thrombosis (DVT) is meant to prevent pulmonary embolism.
There are a lot of questions that she needs answered. Hopefully it turns out being just pregnancy pleurisy and the inflammation will subside with tylonal, antibiotics and rest.