"A girl is not a woman."
Translation:Puella non est femina.
They are not interchangeable. You are encountering a minor bug in the correction algorithm. It allows one wrong letter per word to slide by as a typo, but it's supposed to mark it wrong if that creates a different word in the language.
|I am||ego sum|
|you are||tu es|
|he/she is||is/ea est|
|we are||nos sumus|
|y'all are||vos estis|
|they are||ei sunt|
The verb generally comes last in Latin. But "esse/to be" is a linking verb, so it can come between the subject and the complement (not object, since there is no action to receive).
A change in word order would not change the meaning although it might subtly change the emphasis.