@Regina Bailey - agree with all the above and cash for keys, but you need to talk to her to make that happen so that's your only focus right now. Here are some options to try and get the line of communication going.
Simple enough, try calling her from other cell phones, not just yours. Leave a 5-day under the door along with a note stating you need an open line of communication to figure out a payment plan that works, or will be forced to start the eviction process. This won't count as serving her, but should hopefully get her attention and potentially get her to call back. As @John Warren mentioned, your lease should state you are allowed to enter the unit with 48hr notice so post the notice on the door, text and email so you have all documentation and then show up 48 hours later. Show up on Saturday, evening, whatever it takes, as the problem will only get worse with time.
Getting the convo going has to be your top priority. Some tenants also just skip town so ensure she is actually living there. You can even leave the paper in the door jamb, if it's still there several days later it likely means no on has opened/closed that door.
Once you do have communication lay it out very simply. "I understand you have some challenges, but I either need to get paid, or I'm fine with you just breaking the lease and leaving. If you are not going to do either of those, then I'm forced to go through the eviction route as you've left me no choice. I'm willing to work with you, what do you want to do?" Let her feel some percieved form of control and figure out your next move from there.
Don't start with a cash for keys offer. Hold it close to your chest for leverage and if she chooses the eviction route or fails to adhere to the payment plan offer it one time with a shot clock.
"Listen if you're out by the end of the month, I'll forgive the debt and give you $x for moving expenses. One time deal and have to be out by that date. Let me know, otherwise we'll continue down the eviction path." Too many investors offer it up haphazardly and get taken advantage of.
If you have to evict in Chicago, don't cut corners, and hire an attorney.