Did you miss the part about waiting 18 months for a court date?

A legal contract is only as strong as the incentives to litigate it. Doesn't seem likely a contract would've helped, it may even have existed.

If there was a contract, it probably would have helped a lot in the restraining order hearing. Which apparently had no issues happening faster than 18 months?

A restraining order (at least, a temporary one) can be issued without a hearing.

She had lease with landlord, and was looking to share the place. She was planning on continuing to live in the unit. This is common in a college towns if the apartment is a 2 bedroom, often you would rent the second bedroom out.

Yes, landlord reasonably checked out. They agreed on terms in terms of the monthly amount, utilities etc. New roommate gave some reason to want to get going on getting their stuff moved in or measuring things or something, she gave them a copy of the key for that.

That's all it took.

Yes, sharing an apartment is typical in college. However, when I was in college, it was typical to go to the management and modify the lease to include the extra person. That way they are at least equally legally responsible for everything, and it gives the landlord a reason to care. The landlord may even run a background check, which may have exposed this issue, since you state this was not the first time.

Regardless, tough lesson to learn on not handing out a key to someone without a contract. I mean, that's a level of trust that I don't even have with my friends, much less someone I'm potentially going to room with. No contract, no keys.

I had a feeling there was more to the story. There probably still is, but I'm satisfied now on how this managed to "just happen". I still don't understand how, after the restraining order, this person then claimed legal residence in order to get your friend removed from her legal residence. I also don't understand why this wasn't immediately a phone call to the police to get this person removed from the property.