The accident occured on Highway 116 at Llano Road just after 1 p.m. Thursday.
The truck, which was carrying three men, was traveling west on Hwy. 116 and was making a U-turn when it was struck by the eastbound bus.
The woman was the only passenger on the small bus when it was it.
The driver of the bus and the men in the truck were all taken to Santa Rosa Memorial Hospital where they are all listed in stable condition.
A Sig-alert was issued for Hwy. 116 following the accident, but the road was cleared by 3:45 p.m.