Mrs. Nibbles does not take a tea invitation from the venerable and well-to-do Mrs. Whiskers very lightly. Especially when her two girls are very close to the ages of the Whiskers boys. This tea could lead to a friendship, and infinite possibilities; perhaps even an advantageous marriage for one (or even better, both) of her girls.
"So comb your fur, and wear only your best things, girls. And for goodness' sake... hurry! We simply cannot be late! Hurry!"