That's why is should be spelled as Gabrielle, the double L indicating the pronunciation that you described.
In English, if you spell it as Gabriel the usual pronunciation sounds more or less like "gay-bree-al", which is a boy's name.
I'm Spanish, so I'm my language it's definitely Gabriel and Gabriela, just the same as in Portuguese.
I know for a fact that in French it's Gabriel and Gabrielle, exactly like in English.
Ah, weird names! A family in my country named their son Kevin Cosner (without T) after the famous actor