I think it sounds promising for a coffee date! Definitely give her the chance to reschedule. It's totally normal to have on and off days for fluency. There is no rhyme or reason to mine. It has nothing to do with dehydration, lack of sleep, or anxiety. I used to have teachers that would want it cured or to figure out why. Frankly, I left it to them to struggle with their comfortability on their own. I am not here to make others comfortable because of my struggle. But on that note, I struggle with forgiving people that seem surprised by my lack of fluency. I can see it on their faces. It usually passes, but I see it. It stings every time. Have fun on your date (either this one or the next)! I hope it blooms to romance!