The 9 alcohol meetings stem from reckless driving and two DUI's charges. The 90-day sentence was probably the original sentence before she was put on probation, which the judge likely just reinstated. Which for 2 DUI's, 90 days sounds right on the money, regardless of what 'person' they happen to be.
Which if you factor in the 90-day rehab time, sounds a little more then usually for a first time probation violator. Not sure if Lohan is or not though....