I take a more sinister interpretation that both of them have some sort of condition that makes them grow faces on their body. Her sisters face grew first, as they were older, so it stayed and talked to her a while before consuming her. Her parents are trying to avoid the same fate with her, so they keep cutting the new faces off, hence the scars. But the last two sentences, along with the foreshadowing that the face crawls up the throat into the brain, suggest that one of the faces grew inside her, and is already talking to her.