That doesn't sound strange at all. Maybe Libby learned those behaviors from Dusty, or maybe Dusty is sending you signs through her sister that she's watching over you both from heaven. I, personally, prefer the latter explanation.
I hear you, though. It is bittersweet to see things that remind us of recent losses. I remember the day we put Katrina to sleep, I walked into the family room and got choked up because her favorite chair was empty. When Tigger died, it was at least a week before I stopped routinely checking lumps under the afghan on the couch - he loved to sleep curled up under that thing, and if you weren't careful you risked sitting on him by mistake. Very sorry for your loss of Dusty. I hope both you and Libby can eventually come to terms with your loss. Libby is grieving too, but she is aware of your grief and I don't doubt she's trying to take care of you in her own special way. -Maria
Callie - my dog daughter
Tigger & Katrina - my angel kitties