It is quite simple - it's this (except it can't be, because the Speaker won't let it go again) or it's hard Brexit
I'm sorry but this is wrong on so many levels.
Firstly there can be a third vote. There is two ways to do it, further changes from the eu, which if you read the letter to tusk she has agreed these in Strasbourg already, or she can put a motion to parliament, saying not withstanding the speakers ruling, but we wish to vote again, and if it passes they can vote again on it.
And secondly no it's not this or no deal. There are two other options.
She can do a lengthy extension, likely in return for a second referendum, or she can revoke. And if she doesn't revoke and tries to go to no deal, Parliament can order her to revoke.
So there is this deal or three other options and she can indeed go for a third vote, given certain criteria are met.