Well it's confirmed Raphtalia had the slave curse put back, even though Naofumi felt it unnecessary. And the way she said it sounds like it wasn't even just a way to ensure he'd have no reason to doubt her; instead it sounds like she'd come to view that mark as a symbol of their bond and his faith in her. Kind of odd but I suppose it could happen. Additionally, while I don't know if the slavery affected her growth before, since he's now obtained a slave-master shield I wouldn't be surprised if that has some effects. Just like the herb shields made herb quality increase, it'd make sense for a slave-owner shield to have an impact on his slave.
And wow Filo grew quick. Three days to go from an egg to a giant that could eat a moa to a loli angel. I'd have thought it'd take at least two episodes for that much growth to happen. And reading the manga, one thing I noticed they cut out was an odd trait of filolials: