The first time they were late should have been the day they were locked out, the locks changed, and their belongings packed up and put in a storage room until they paid.
I suggest she do that now.
She's got a lawyer. What she should do now is consult the lawyer. That's what the lawyer is for.
There is an important legal prinicple here: in a number of states, hotel customers that stay for extended periods of time, say more than a month or two, are quite often regarded as tenants rather than guests. Once they are regarded as tenants, the innkeeper (who is now in the role of a landlord) must use the eviction procedures to get the tenant out.
Whether a person living in a hotel/motel is a guest or a tenant is something that is resolved by the courts looking at case law; it won't be found in the IL statutes. It is not necessary to have a written document with the title "lease" on it to create a lease. At least one IL appellate decision held that persons living in a hotel for over two months were actually tenants, not guests. The fact that they have been living there well over a year probably weighs heavily towards finding them to be tenants, but the details matter.
She should understand that if the law is not clear and she chooses to simply lock them out rather than go through formal eviction, she runs a risk that a court might rule against her if the guest/tenant sues and determine that this was a tenancy, not a transient guest situation. On the other hand, if she evicts, while that takes a bit longer, she doesn't run a risk of being held to have unlawfully ejected these folks.