[X] Plan: Open and honest
[X] Ask Maya what's wrong.
-[X] In fact, hug her again. Couldn't hurt.
--[X] We thought she was keeping it a secret because no-one else could do this, and told us because we
can... so we figured she'd be happy to tell Dad since
he can do it too.
---[X] If she insists, then we won't insist...
----[X] ...But now we're worried about having told her that Dad can do it too without him knowing. It's a secret to everyone!
-----[X] If everything is said, done, and resolved, tease her. "So...you think I'm pretty?"
Okay, I like the last line of your plan so I added it to mine. To anyone who's unsure of the differences, WUTB's penultimate vote is this:
----[X] ...But now we've told her that Dad can do it too without him knowing, so she has to keep
that a secret too! It's a secret to everyone!
The difference is that my plan leaves the way open for her to consider her position, in case it was a knee-jerk response to someone else being informed, whilst WUTB shuts down the "telling Dad" option entirely. I argue that giving Dad the
option of either informing her about the Masque and Saiyans, or simply running with our story and helping us keep it straight, is superior to WUTB's complete backtracking on that point.
@Andres110 (and correct me if I'm wrong) is concerned about the possible negative consequences of her discovering the Saiyans, which I think he is overestimating but which is overall fair enough as a position. But I would argue that if those consequences
were to come about, Dad would instead choose not to tell her about the Saiyans in the first place and would instead help us with our story, as he doesn't want bad things to happen to Maya either.
TL,DR: If telling Maya about the Saiyans and the Masquerade would lead to Bad Things happening to her, Dad will choose not to tell her about them and will instead simply help us come up with/maintain a story.