Put a lien on the property(s) they own, this is needed by some court action (i.e. lawsuit in civil/criminal court) 

They've been very underhanded and petty though, I do expect a court filing if we simply ignore.

My question is if she doesn't pay in 5 days, could I file a forcible entry detainer at the court ( We are in Macoupin County Illinois)?

That outlines who gets what, and you avoid probate court.

I don't try to evict based on neighbor complaints as those aren't super reliable and the people likely won't show up to court. 

Give it time, this is getting shredded in court as we speak.

The best way to learn this is by reading a Tax Court case.  

Squatters can now be locked out of a property and their possessions removed, but a landlord CANNOT physically remove the squatters themselves.The local police are supposed to enforce these laws and assist landlords in removing squatters.The reality is that when you call the Detroit Police to remove squatters:1) The police often don’t know/care about squatter laws and state you must take the squatters to court to evict them.

Why wouldn’t you go to court?

https://natlawreview.com/article/texas-federal-court-issues-nationwide-injunction-against-enforcement-corporate