My dog has depression since I've left home

So I've moved out from my mothers house. Everything is golden, minus the dog. She has since developed a deep deep depression, and will not be happy at all unless I am in her presence.

Just for clarification, my dog is named Sally.

My mum has always been close with the dog and they absolutely adore each other, however I am probably the "fun" side of Sally.

My mum can throw her ball as much as she wants but she just doesn't react the same as when I am there.

Does anybody have any ideas on how to get her out of this? Or perhaps keep her happy for a while after I leave (as I pop in every few days)