Rosa could still be living. Unfortunately I'm much better at locating dead people than living ones. Additionally, depending on the jurisdiction, her records may not be available to the general public due to privacy concerns.
Have you google'd her? Joined an Illinois genealogy group on FaceBook or Rootsweb to see if someone there can help? Searched out old phone books and city directories at a library?
I'm assuming you've checked the 1930 and 1940 census (available for free on FamilySearch.org and know where they were living at that time. Ancestry.com has school yearbooks and city directories which could be of some help.
That's about all I can offer. Sorry.