I’m sorry to hear of Ella’s passing. When I check in with Dante, he looks very confused and lost with Ella’s passing. It’s not something a new dog will address, though. He doesn’t have an understanding of what happened to Ella or where she is. In Dante’s eyes, she was there one minute and gone the next. Take some time to sit with him and explain what happened. Use your normal voice–not the sing-song voice we use when we’re telling our dogs how much we love them. He is also experiencing your grief, confusion, and guilt – Dante is very open to energies and feels everything, but doesn’t always understand what he is feeling.
In addition to speaking with him I suggest you work with some flower essences, which work vibrationally, to help support him. As natural remedies, they help if they are needed and they do no harm if they are not. I recommend the Flower Essence Society brand, they offer a more harmonic vibration than Bach. I recommend five drops three times a day of Gorse (for depression and despair), Star of Bethlehem (for comfort and reassurance), Pink Yarrow (to help him address his openness to energies), and Mimulus (for courage).
It looks like it will take him a few months to process her loss and then you can begin to consider a new friend for Dante. Animals experience their own grieving process, so it is important to let Dante have this time to mourn the loss of his sister, but as I already mentioned he does need help in understanding what happened and why she is gone.