It's been a long time since I got really drunk, but yeah, your memory does return in dribs and drabs especially as people fill in little details and it starts coming back. It doesn't really surprise me that she would remember more after reconstructing events than she did that morning.
Jen McCabe stated that Karen thought she last saw John at the Waterfall, until Jen reminded her about being at 34 Fairview.
Hey, if you want to convict her for drunk driving, you'll get no argument from me. She likely drank too much and should have never gotten behind the wheel. But I don't think her swiss-cheese memory is evidence that she committed murder.