Going back to 2018 a study was conducted on Chester's herd and their dynamics.
Maya directed most of her interactions towards the calves at the time (so Nandita, Indali and Aayu). She spent most of her time with Aayu (which made sense considering his mother was a bit of a wanderer herself), then Thi and then Nandita.
Following the death of two of the calves (Nandita and Aayu), she consequently directed more of her attention towards Indali especially, and also Thi and Anjan. However it was noted during the latter half of that study that she began to get frustrated with Indali often and proceeded to display aggressive behaviour towards her. Likely attributed to Indali constantly badgering her more for attention after losing her two playmates.
Evidently, Maya does seem to be fond of calves the most so it would be good to have calves in Chester's herd again! It was noted her emotional stability also decreased following the deaths of the calves, indicating their importance to her.
The study also noted the adult Aung Bo most interacted with was indeed Maya, so I'm not sure whether there was a falling out between the two in recent years (perhaps following Thi's passing?) or whether there was another reason why the two began to spend time apart.