senior property tax freeze in cook county

My neighbor's house was misclassified for 50 years as a two story with full basement when in reality her home is a ranch with a full basement. This resulted in her home being over assessed by 1200 sq. ft. of living space since basements aren't considered living space for tax purposes in Cook County. This error was corrected in 2015 and and a certificate of error was also filed for 2012,2013, and 2014 and rebate checks were issued. But here is the question: The assessor's office reduced the assessed value down to 35K for 2012 and 2013 from an original assessed value of 108,000 and since she had appealed her assessment in 2014 with the Board of Review, that successful challenge to her 78,000 assessment in 2015 result in an assessment of 68,000. Does the senior freeze only freeze at the original date you you filed, in her case being 2008 when her assessed value was somewhere in the range of 165,000 or will it automatically rvert to the previous year to the current year she is applying the freeze to? Is she better off not freezing her taxes and just keep challenging her tax bill from year to year? I'm confused why her taxes didn't freeze at $35,000 assessed value when the assessor lowered it in 2012 after successful appeal. Is she being "frozen " at 165,000 if she keeps applying for the senior freeze? What is her best strategy going forward? Does she have any legal recourse for the fact that she was over assessed for that many decades due to an error on the assessor's part? I feel the assessor's office owes her much more rebate than going back 3 years when it was an assessment mistake to begin with. At the minimum , she should get a lower assessment moving forward. She is 92 years old and on a fixed income.