Who has section 8 rentals in Chicago?

[Ori Foyer]

My tenant moved out on the end of June, I rehabbed the property and plan to sell it. At the beginning of August the tenant get in the property with the keys she has and doesn't want to move out since than. My mistake is that I didn't replace the locks. Based on Section 8 the notice period ended at the end of August  (although I sent them the relevant documents on April) and she has a ready to get in property since September 1st. 

She always stated that in two days she is going to move out, but keep staying in my property. Section 8 warn me to not stopping the utilities, otherwise I'll get a fine. 

What else I can do to force her move out? 

Any advice??