It's a correct sentence. (and not idiomatic in anyway - ragazza is commonly used to mean girlfriend as well as girl)
Whether or not it is a sentence you would ever need... well.... it's probably on a par with other Duolingo gems such as "The elephants are yours" or "The turtle does not read"
The way one of my Italian friends described it was: if you were speaking fast, like in French, you kind of blend some words together to be able to flow better off the tongue. I'm a native speaker from quebec city, and in the same situation qui é, would be pronounced like they were together, but they aren't written together