She does look lonely mate, but hopefully there will be a couple of rare clones going in there soon to keep her company.
Yea with the roots at the top thing, on every re-pot i always had an inch or two of unused compost at the top with no roots in, probably up to 20% wasted pot volume, this way maximises pot space and root amount, and we all know more roots mean more yield
She will officially become a mum when the current SOG is about a week or so from finish, il take 25 clones from her, root them then straight in to the 6ltr pots, no potting on, maybe 2 days of 18/6 for them to get used to the pots then 12/12.