I wonder if we're supposed to 'know' that it's Sylvie and it turns out that the person she is living with is actually her lesbian lover. She has previously denied being a lesbian, but there was a small hint a while back when she shared a knowing laugh with Tina, and then tonight when Tosh said "YOU sent THAT message?"
Of course, we don't know that Babe is an actual blood relation of the Carters... it could well be that the 'Aunt' is a familiarity rather than a blood-related title, and that both theories are right: Babe is living with her lesbian lover - Sylvie Carter!