score:4
The short answer is no. There are many reports of people "seeing" Heaven or Hell and coming back, but as for entering, there is no return. That being said, Heaven and Hell are spiritual states (at least before Second Coming/Apocalypse) and not physical places; so, in theory, being in Heaven or Hell would rule out "presence" (in a non-physical sense) on Earth.
Take miracles which are attributed to saints. Such happenings suggest that human souls in Heaven can have some effect on the physical world. This being said, it seems much more common that spiritual interactions on Earth are on account to angels/demons.
But coming back as a "ghost", that is, a human spirit that has physical presence on Earth is not possible. Accordingly, I do not think there is a definitive answer to the nature of the "presence" which your room-mate feels; though I would be careful considering it to be her grandfather himself.
--Roman Catholic