Strange questions.

Aww your welcome and blessing of the moon ^-^

Ya, I've had many experiences with spirits over the years.

the worst was an alter of me from a past-life,
since it was having so much trouble re-integrating,
with this sterile society of mass indoctrination (schools, media).

anyhow ya, any creature will leave if you ask it to,
if it resists leaving tell it about karma,
and that if it wants to be able to banish,
then it must allow itself to be banished.

how I explain it to spirits that don't use language,
is imagining a bigger spirit intruding on them,
as if to say "see how you'd feel",
they usually quiver, and flee.

Though yes, salt, or a circle by any means,
can help to physically define a perimeter,
however if she already has walls and doorways,
those work also, can enchant the walls and doors,
by singing to them, and casting spells
that they protect you, are strong and loving,
only allowing beneficial spirits entry.

Hmm. It does seem like from what you've said it could be a harmful spirit, but I am not sure.
I have seen things terrifying like that before. GIven me that horrible feeling.
If you could ask your friend to take some photos of her room and send them to me. I can sense spirits extremely well, even through photos, and I may be able to help.
I am a Necromancer, and have spoken with many spirits. Some good, some bad. And I would really like to help your friend.