Either rehab or plastic surgery. But in either case why dont the Clintons make an announcement of where she is? She has just dropped of sight, which seems very odd for a presumed presidential candidate.
Hillary was meeting with another BJ (not Bill) yesterday, so it’s not like she is on a news blackout or anything.
http://www.theguardian.com/politics/2015/feb/11/boris-johnson-sings-hillary-clinton-praises