Flea bites and Enbrel

Today one of my Enbrel patients showed up for a regular visit. Three months ago she had bites all over the body, most bites on her legs. Someone suggested bed bugs (Cimex lectularius), but I thought of flea bites.
She is 59 years old, suffering from rheumatoid arthritis and is doing well on Enbrel for a couple of years now.
Today she told me, that her bites were flea bites indeed. The interesting part of the story is that no one else besides her got bites, not even her husband, not friends or relatives, not even kids rolling around on the carpet. She had to call the terminator, no make it the pest exterminator. He had to come twice. And he identified the culprit as the European chicken flea (Ceratophyllus gallinae).
But the question still remains, why did she get the bites and no one else?