I'm just figuring that she was trying to pre-empt any complaints about Brexit in advance by making sure she had a mandate.
But, other than that, I don't really understand why she called an election - I agree with you that May was trying to seek a public mandate for her version of Brexit.
But I believe there's more to her decision to call the election.
At the time, the Tories were enjoying a huge lead in the polls over Labour (20 points) and I think May saw this as an opportunity to crush Corbyn and Labour underfoot. This would then give her a mandate to do whatever she bloody well liked for 5 years.
It's completely blown up in her face (*snigger*) and I think she definitely won't last 5 years as PM.
She deserves to go but I think other Tory MPs are stuck between disposing of her and allowing her to continue.
I'd imagine that May wants to carry on for 5 more years as PM but most of her colleagues want her gone within 6 months.
PS - you're not a dumb American. You're quite a perceptive one.