I have, literally, an entire notebook trying to figure out my "plot." I did several exercises, took notes, jotted down anything that came to mind during the writing. My major dramatic question started off as very personal but it's changed and evolved over the writing and now it's opening up into something more universal. But it took 75,000 words to get there, and I'm not finished, so it may morph again.
Tell your friend not to fret too much about plot. I know it's hard because at first I really stressed about it, but mine came to me through the writing. It was a slow process, a building. Just because it's memoir and we're using "real events" from our lives doesn't necessarily mean we know how the story ends. I'm 75,000 words in and I still don't know. That's become the reason for writing--I want to know how it all ends--and I'm not talking about the "event" that ends the story, I'm talking about the emotional story, what those events mean to me NOW, how I interpret them. For me events are just events, the story is figuring them out.
But that may not be very helpful, and I suppose if someone had told me that when I first started writing the memoir, I would've rolled my eyes and thought: How do I friggen plot?!
A couple exercises I did:
Timeline -- Graph events on a timeline. Don't leave anything out. You don't have to use everything in the story, but sometimes small events that seem meaningless are actually significant or they trigger something significant in your memory.
Big events/Turning points -- jot down the big'uns. They can serve as anchors. More than likely you won't be able to use them all, but there could be a connecting thread between several that can serve as a subplot or major dramamtic question. For example, in my "Big 5" one of the common threads was a loss of innocence.
Reverse Plot--If you know which event ends the story, take that event and plot backwards. Ask yourself what CAUSED the final event. Write it down. Now ask yourself what caused that event and write it down. Keep doing this until you get to the source. In my case, it went all the way back to events that happened before I was born.
Hope that helps and good luck to your friend!