Awe bless, my father inlaw also has lung cancer, he is taking warfin.
She needs to consult with a cardio, which should also be talking with her consultant for her lunc cancer.
Her cardilogist/pcp should be making these decisions, not an ER doc.
From what I understand I think the doctor should be told of the severe side-effects of the current medication and ask if a "softer" medication can be taken. I would also ask about an anticoagulant. You didn't mention Coumidan/Warfarin. I think at age 79 use of a simple aspirin as an anticoagulant would not be sufficient. Those are some suggestions on questions/facts to bring to the next doctor visit.