Your an idiot, your trying to have such an important conversation over TEXT messages? How many times do guys say on here, don't get into their texting games, its how they can control the convo without any confrontation.
If she texts, don't respond. She will eventually call, when she does call, start acting like a man and deal with the situation. Tell her that the next time she is in Chicago, you want to go to a doctor's together and get the test done. Then tell her after you see the results, you and her will have a talk and discuss your future.
Don't tell her your going to dump her azz if its negative, thats only going to rile her up more. Just tell her you will discuss YOUR future together and how you want to proceed after the test.
Then dump her ass & cut all contact when it comes back negative.