Was just looking it up when you sent your link. All clear now. I never knew there were two queens but don't think I ever read the sequel as a child. Thank you for that.
As you have correctly deduced the screamer is the Queen of Hearts. She screams the 4 words in 1 Across. To find out who she is screaming about, look up the title of the puzzle, and reverse the 4 word instruction with A....