OK, I looked it up, and it can happen. It's a very rare condition, and it is extremely serious, so she should get herself checked if she hadn't already.

Look here:

http://www.ncbi.nlm.nih.gov/pubmed/3605561

"Cardiac herniation is a rare but dramatic complication of pulmonary resection that demands urgent treatment. About 50 patients have been reported in the literature; 50% of them died. Symptoms vary depending on the location of the pericardial defect. Cardiac output falls, central venous pressure rises, and cyanosis develops that does not respond to oxygen administration."