Stacia stands up on her toes so she can get a better angle for the hug, sliding her arms between his arms and torso so she can give him a proper hug, one of the ones you can still feel after they've finished. It's not generally a hug shared between two relative strangers, but it's the hug Stacia uses for First Changes and when someone has died. Firm but not crushing, and she's letting Remus decide when it's done.