Ive just replied a post similar to this,I must be eager too get my views across. 🙂
Anyhoos…
I like to think that Regan found the crucifix as she was demonacally desocrating the church early one moring.
And therefore scuttles down the stairs(probably right on her mothers coat tails)to retreive the crucifix as she and kinderman disscuss denning`s death.
Also later in the film when Regan is suppossed to be secured in her bed,we see her shadow moving around her room…which I find a little freaky.