
I'm in the same boat.
I lost my TM to cancer just before Christmas, then my SBT in April, now left with one very unsure little SBT girl.
It takes time, and the time will be different for every dog, and the severity of the lose. I've been concentrating on play for my girl Daisy, play can have a remarkable effect on dogs, one which I think can be over looked. It can reduce stress, and improve the trust and bond between owner and dog, and improve confidence, which is precisely what a dog needs at times like these.
Don't confine yourself to just chasing a ball, play hide and seek, scent work games, puzzles, box diving ( big cardboard box, lot's of scrunched up newspaper and treats = hilarious fun ). Have a look on line there are bound to be lots of idea's out there.
Visiting people has also been a big favourite with her, we always did it, but not so much with three dogs in tow, one of them being huge and hairy.
I was concerned too about leaving Daisy on her own, but she hasn't been troubled by it at all, like your doing, I started out small and gradually built up the time.