The late model's former companion and attorney Howard K Stern and her psychiatrist Dr Khristine Eroshevich were found guilty of conspiring to give Smith excessive amounts of prescription medication at a jury trial two years ago.
Eroshevich was also convicted of a count of felony prescription drug fraud.
However, the conspiracy convictions against the pair were quashed by a Los Angeles Superior Court judge in January 2011 on grounds of a lack of evidence.
Eroshevich's fraud charge was also reduced from a felony to a misdemeanor at the same hearing.
[Anna Nicole Smith and Howard K Stern, photographed in 2006]
The 2nd District Court of Appeal has overturned the conspiracy acquittals of Stern and Eroshevich, and the original trial judge now has several options available.
These include sentencing Stern to prison or probation on the basis of the original convictions, considering Stern's request for a retrial or finding other legal grounds to dismiss the case.
The appelate judges noted that retrying Stern would constitute double jeopardy. However, Eroshevich is eligible for retrial on the original conspiracy charge.
Smith died of an accidental overdose in February 2007 at the age of 39.