I think it would be interesting to know how much involvement her editor at Penguin had.
It may be that Salray got into a position where she had to either admit she was lying or continue, and her inclination is to add to the lie with a bigger lie.
I'm reminded of a time in Brownies, we were playing a game where the leader asked a question (eg who was born in June of July?) and threw a ball, and if the answer was "yes", you tried to get the ball.
I'm a slow runner, and not particularly good at catching, so I had very little chance of getting the ball anyway, but all the questions Brown Owl asked, my answer was no. So I decided the next one I would go anyway, just for the fun of moving.
"Who has done some shopping for someone else today?"
So they asked the question, we scrambled for the ball, and as luck would have it, the ball bounced off someone's foot and landed literally at my knee. I couldn't have not grabbed it without it being clear I was deliberately not taking it, so I took it. Brown Owl asks "did you shop for mum" (which might have been believable), and I went into a long story about how I'd gone to buy a toy car for my brother - so clearly a lie that it was probably seen through by the entire room. Brown Owl pretended to believe me, and at pick up time I was desperate to make sure I got Mum home before Brown Owl said anything and found out I'd lied.
I wonder if it was a bit like that.
Salray submits the story of walking the path as a basic story. But when she sends it in she writes a query letter that is designed to get sympathy.
She explains how they were homeless, and Moth wasn't well, so she so hopes they will accept her story.
It isn't a part of the story that she is expecting to get public, but she's using it to hope that an agent will feel sorry for her and look further (like me going for the ball, not expecting that I'll have to justify going for the ball).
The agent however sees this as a potential story so asks about it. She has to answer (like me having the ball land directly at me). So she embellishes the homeless (it was just so mean and not our fault at all) and Moth's condition (making it terminal) thinking that makes it more sympathetic and more likely to publish. (like me - embellishing it thinking it sounded better)
The agent then tells her that the story is publishable, but only with those details to make the books sellable. (she didn't have the option of grabbing Mum and getting away).
But she's then in a position. Does she admit she made those two things up and then the agent will not want to work with her to publish the book, or does she add it to the book with the risk of being found out?
And she chose to add it to the book.
So it wasn't in her plan, but once she'd told the initial lies, she couldn't stop it going public without admitting it wasn't true.