If you want to really pursue it, I'd say ask a lawyer (but you'll probably pay them the same amount you're losing...).It sounds like she is following the rules for notifying you 30 days in advance."

I am not a big fan of many of generic rules but the 50% rule (cost not including mortgage associated costs (PITI) is ~50% of rent) I believe to be semi accurate in low rent locales. 

If you do close on this place with the tenants still in, make sure to conduct a background check and follow all the rules you would for screening new tenants. 

Spend some time on google I’ve never checked Chicago but most cities have rules against short term term renting or what has become known as “AirBnBing” Especially apartment/condo STR.

As I’ve been evaluating deals I’m trying to follow the 70% rule.

It seems a little bit like the 50% rule.

Based on your numbers the "70% rule of thumb" would come to an offer of 27k, but that is just a guideline.

As a general rule I only recommend portfolio loans to experienced landlords who already have at least 2 properties and preferably 5 years but at least 2 years of experience.

So I find that when I evaluate properties according to the BiggerPockets method, including CapEx monthly, including 5% of gross rents for repairs and maintanence, including 10% for property managers, etc, NO property passes any test.  1% rule, 50% rule, or even being positive cash flow.  

I have recently found some properties in my target locations meeting the 1% rule.