Don't know about her, but that is definitely NOT the only way one can get possessed.

It is one way, however. A major way.

Another way: using heavy drugs -- INCLUDING anesthesia.

So if you've ever been under for surgery, that's a chance for demons or other negative spirits to walk in.

Sometimes it can just be a person who died but doesn't realize it and steps into your unconscious body.

Your auric door is open although you did not technically invite them.

Hospitals are full of wandering spirits.

Another is trauma -- that leaves holes they can slip through.

Head injuries, very definitely.