Jacquelyn Allen-MacGregor, 47, also was ordered to pay $2.08 million in restitution and serve three years of supervised release after her prison term.
Allen-Macgregor was employed by the Capital Area United Way in East Lansing for 20 years before resigning as vice president for finance in November.
She pleaded guilty in February to check forging and engaging in an illegal financial transaction. Prosecutors said she stole the money over nine years, beginning in 1994, and used it to fund her quarter horse business.
Standing before Judge Gordon J. Quist, Allen-MacGregor apologized to her family, the charity and its supporters.
"I do believe that I'm obsessed with horses," she said. "I'm just starting to understand why it happened."
Allen-MacGregor's lawyer, Brian Morley, characterized his client's behavior as "an addiction" similar to compulsive gambling and told the judge there was no other logical explanation why someone with no previous criminal history "would commit a fraud of this magnitude."
Morley argued that Allen-MacGregor should receive a more lenient prison sentence than the 41 to 51 months called for under federal guidelines because she cooperated with authorities and spent virtually all the money on horses, not herself.
U.S. Assistant Attorney Daniel Y. Mekaru, however, encouraged the judge to stay within the guidelines because many convicted thieves have stolen money to buy objects they were equally compelled to possess.
Mekaru also said the United Way theft badly tarnished the charity's image and hurt its ability to solicit donations.
The judge did grant Allen-MacGregor's request to remain free until she reports to prison.
By James Prichard