"彼女はなんて美しいの?! ((でしょう(か) ?!))’’ is correct
"彼女はなんて美しい" is not correct while 彼女は美しい is correct
なんて・なんと(いう)ふざけた話((なんだ?/なの?)だろう!)) What a ridiculous story/situation
*だろう has three meanings:
1) そうだろう?It is true, right? 2)そうだろう。It must be true. 3)そうだろうか?Is it really the case?
なんてうるさい犬だ! What a noisy dog!
↓
なんてうるさい犬(なん)だろう/でしょう(!)This is without exclamation mark and is just a statement but has certain amount of emotion.
なんというなまいきなガキKidだ!
なんてなまいき(生意気Cheeky)なガキだろう(!)
I can't explain grammar sorry. Btw, if people aren't answering, you should resend your question after two days.