I agree, it is the funniest thing. My sister's dog tattles too. The first time she did it I didn't believe that's what she was doing but I've seen it so many times now. If any of the animals are doing anything she knows is wrong she will bark, run over to you, then back to them and bark again. She's always catching Gus trying to get in the garbage.
That's great Sassy is adjusting so well. They'll be best friends before long.