In reality she wasn't. But popular imagination has always seen her as that. That's the Elizabeth of Blackadder, it's (with varying degrees of concession to historical reality) Cate Blanchett's and Glenda Jackson's Elizabeths, I'd argue that it's there in Flora Robson's Elizabeth, and in a way it goes back to the romanticization of Elizabeth by Spenser. Elizabeth was a mistress of her own propaganda, and her image has been pretty much set in stone since then (with, I suspect, a big boost in Victoria's reign).