I'm so sorry for your loss. Your Cleo reminds me so much of our Lab/B cross, Kia. At 13, she's starting to get stiff and impatient with her two Basenji brothers, but she's also been a kind and patient "nanny dog" to a number of lost-soul male Basenji fosters.
To suggest an answer to your question, same sex dogs don't always bond as well as opposite genders. Kia and my first B, Sam I Am, never got along–both females, so not surprising. And most of my male foster/forever Basenjis have worshiped the two females--but only tolerated each other.
But don't be surprised if Bassit starts displaying Cleo's mannerisms or behaviours if you ever adopt a little brother for her. When my Sam I Am passed away, very uncharacteristically Ben took up her duties as "Little Mother" to the next foster, surrendering his food bowl, cleaning and hovering like a mother hen-- with the same devotion that Sam had lavished on him.
