It is possible for your aunt to be contacted, even if it seems unlikely. Accepting means tested benefits, if this is the situation can create challenges and delays in processing. In these situation, attorneys should be careful not to use a crystal ball and try to act as a fortune teller.
The Government has the right to use a particular case as an example. The Government does not need to consistently enforce the law. The Government has the right to enforce the law as it sees fit.
Only means tested public assistance can create challenges. The other issue is whether you are likely to become a public charge at this time. Past action can have an impact. Since you 'may' have already taken means tested benefits, an I-864 sponsor or co-sponsor may have concerns.
The U.S. Government may have to go after the sponsor for the funds. This may not happen, but if it does can be devastating to a sponsor. The laws allow for such an action. It is unclear whether the Obama Administration or Congress will fund such a program to seek reimbursement.
The concern is whether you had to demonstrate poverty or low income in order to qualify for Medicaid assistance. Emergency medical assistance should not disqualify a candidate for immigration. If you have any forms that you filled out, then you should try to find an experienced attorney who is willing to take a look at the documents. Some not for profit organizations may have an immigration attorney program to provide free legal assistance.
This is general information and is not meant to create an attorney-client relationship.