MRSA or methicilin resistant staph areus is a bacteria that is fairly resistant to many antibiotics. It can be diagnosed with a swab of the affected area (or if it is in the lungs, a sputum sample) and cultured out in a lab.
You don't have to have sores on the skin in order for MRSA to be present in the lungs, that much is certain. I am not a doctor, just a former nurse who helped treat people with MRSA in their lungs...they were usually people who were immunocompromised somehow either by age, previous lung disease such as COPD, or other disorders that affected their immunity somehow. That's not to say that a healthy person cannot get MRSA in the lungs, I am just saying that the population listed are more predisposed to that type of infection.
I would say if she wanted to be sure, have her doctor get a sputum sample , being that she has pneumonia she probably has a productive cough and could give a sample easily. The lab will then culture it out to see what the offending bacteria is as well as be able to tell if the current antibiotic will work or if it needs to be changed out for a new one.
I hope this helps...good luck.
Jenn.
Oops, spelled staphylococcus aureus wrong in case you wanted to look it up.