First we must find the beginning and end by looking for the capitalized word, and the period.
All of a sudden, = for dance practice.
Now we can fill in the other sections until we find the only ones the fit smoothly:
All of a sudden, she realized it was Monday, and she was late for dance practice.
This is the answer. I underlined every other section of the sentence, just in case you need to see where they split.
good luck <3