In April, Bridget McDermott was a prisoner at Coffee Creek Correctional Facility and expected to spend another six months there before her release, which the corrections agency projected for Oct. 4.But the prison’s calculation was wrong. She spent an extra 21 months in Oregon’s women’s prison when she should have been free, after serving about 14 years on a 2010 robbery, burglary and kidnapping conviction in Lane County.Her best friend died whil…