How to make randomly pop some gui without stopping the script #python 2.7

I'm relatively new to python, so please bear with me.

My question has two aspects:

• First, I'm trying to make a GUI that randomly pops different sentences to the user, every time in a new frame.

• Second, I want the user to be able to close the GUI without stopping the script, like if it was running in the background.

here is my code:

import Tkinter as tk
import random
number = random.randint(0,13)

sentence = {contains 13 sentences
    }

window = tk.Tk()

window.output = tk.Label(text = sentence[number])
window.title("I Always See You")
window.geometry("300x150")

def next():
    rand= random.randint(0, 13)
    window2 = tk.Tk()
    window2.output = tk.Label(text = sentence[rand])
    window2.output.pack(side="top", fill="x", expand=True)
    window2.title("I Always See You")
    window2.geometry("300x150")

window.output.pack(side="top", fill="x", expand=True)

choice()

window.after(1000, next)
window.mainloop()

My problem: when my second frame pops, there isn't any text showing, and if it does have something popping, it appears in the first frame.

also, how can you insert a random float in .after() ?

Thank you so much for your help!

cheers