What can friend legally do about a tenant?

I'm posting on behalf of a friend. She rented out her property on Booking.com for 1 day to some tenants. They extended to 2 days, then extended again to a full month. They have NOT paid a single cent for any of it.

Now things have escalated. They are threatening her with violence, demanding money from her and being generally aggressive and intimidating.

She wants to get them out and report the threats, but she has an illegal water and electricity connection on the property (bypassed meters). She's absolutely petrified to involve the police or any authorities because she's scared of getting arrested or slammed with massive fines.

What can she legally do here without getting herself in deep shit?