A 34-year-old woman was sentenced to 50 years in prison for her part in what federal authorities described as one of the largest income tax frauds ever uncovered in Southern California. The sentence imposed on Barbara Ann Woods of Los Angeles, who pleaded guilty to five counts of filing fraudulent income tax returns and five counts of mail fraud, can be changed after a 90-day psychiatric study is completed, Assistant U.S. Atty. Sharon Ellingsen said. U.S. District Judge Matt Byrne imposed the maximum allowable sentence so the woman could be examined, Ellingsen said. Woods was indicted in June for allegedly filing more than 100 fraudulent income returns claiming $300,000 in refunds.