Risk to waste a daughter on an inferior match as that girls can be married better (aka to a ruler who can be an useful ally for their family)Where is the "risk" for Florence?
Where is the "risk" for France in giving their hunchbacked daughter?
Duarte is a royal Duke and not some Duke whose own Duchy is overtaken by someone else.
Claude can still marry a ruler (Lorraine or Navarre) and in any case marrying a vassal of her father is better for her future and more useful for Henry/Catherine than gambling on Duarte’s possible inheritance...
(If you want Elisabeth for Duarte kill off don Carlos, Mary I of England, Henry II of France and the Dauphin Francis in quick succession so Philip II will remarry to Mary Stuart instead of Elisabeth of France)