She's not. If Democrats give in to the demands of Pres. Trump it will only embolden him that his methods work. Democrats have nothing to lose, they passed a clean bill, they offered money for border security, etc. Democrats tried negotiating in good faith, Pres. Trump has his opinions literally dictated by Fox News and right wing pundits, which means that even his own party can't even count on him.
This is entirely meant to be a distraction from the Mueller investigations so Pres. Trump has no vested interest in ending it. He had 2 years in which to get the funding passed unopposed, he chose not to. This is entirely a manufactured controversy intended to distract. Anything the Democrats did agree to would immediately be thrown out by Pres. Trump. The only person who can end the shutdown is the President.