The first blonde does a silly thing by sending the kid home.
The second blonde does an even sillier thing by paying the money.
The joke could have ended there.
But Blonde 2 is simply making an appeal to kinship - perhaps implying that blondes should "stick together" to overcome the prejudice of others. But that line (and the note) also balances the joke, and stresses further how silly Blonde 2 is.
PS: I like the joke.
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