Time Lords were telepathic, usually only mildly. The human capacity for telepathy tended to begin and end at identifying psychic paper as such.

The Doctor had left Ace here, as Rani's ward; had warned the Rani that if anything happened to his Companion, the Daleks' fate would be mild compared to Rani's.

So Ace stayed in the labs, as did the Rani, working at all hours of - well, there was no day or night, not here, on a world tidally-locked to its red dwarf sun.

But on those rare moments when both women sleep - usually on opposite ends of the facility so they don't kill one another, regardless of the Doctor's orders - their minds touch.

It's why the Rani permits Ace to try her hand at refining the chemicals that will end up in the next walking weapon that her lab will supply for the Time War...based on chemical-squirting beetles of Earth, fittingly. The Daleks shall puzzle over this, no doubt, which amused Rani, and was why she permitted Ace these liberties.

Ace has other thoughts in her sleep, other reasons why the Rani tolerates her. Doctor! which runs through the Rani's own thoughts; they both know the Doctor, both feel for him, both have measures of feelings for him.

Shared feelings, both before and after their minds touch at a physical distance.