She was ill yesterday,so she lay (为什么不用laid) in bed for the whole day?

问题描述:

She was ill yesterday,so she lay (为什么不用laid) in bed for the whole day?

这里的lay是lie(躺)的过去式,而你说的laid是lay(放)的过去式.
她生病当然是“躺在床上”,而且lay是及物动词须有宾语.