Interesting article I just read concerning Trump going the national emergency route. It appears that Congress, either the House or Senate has the ability to end a national emergency by putting it to a vote. So there is a provision within the national emergency act that allow either the House or Senate to produce a resolution to end an emergency declaration. The law itself sets a max limit of 6 months before the Senate or House must vote on the continuation of an emergency but there isn't any sets on the minimum.
So what that means is that Pelosi could do is immediately call a vote within the house to end the emergency and then it gets sent to the Senate. The Senate has 15 days to vote on it and they must vote so McConnell cannot deny bringing it to a vote like he has with the other bills to open the government. There is already 12 Republicans who are on record who are not sitting well with this plan from Trump so things could get very interesting if Trump does decide to go the emergency route.