Fannie Mae doesn't make the original loan, not do they service a loan, but they do purchase the debt from the bank that originated the loan. I am guessing that is GMAC.
In a foreclosure, the deed of trust held by GMAC needs to be transferred to Fannie Mae in a legal document for them to foreclose on it. It could take a few days or weeks to get it approved, but with closer scrutiny on foreclosure proceedings, it could take longer. Hard to say.