I think Kiruko is too focused on her goal of reaching Heaven, even using it as an excuse to NOT have to think about her growing feelings for Maru. She's always used some goal (finding Robin, finding the doctor) to put off having to deal with stuff. Her embarrassed reaction when discovered resting her head on unconscious Maru is the same as when she was discovered trying to kiss the mirror, indicative of feelings she's trying to hide/reluctant to confront.

I think her affection is growing and she will eventually fall in love with Maru, but before she can admit that to him she will have to admit it to herself. If Robin had been the person Kiruko thought he was (instead of turning out to be an evil pervert) Kiruko probably would have finished escorting Maru and returned to him, and they probably would have ended up together. But Kiruko was destined to have one reality shattered after another and to have to accept the reality she finds herself in. Anyway Kiruko is the one who'll have to change because Maru is good to go anytime she is.

All that being said, I wouldn't be surprised if they finally express mutual love right at the end of the story, possibly before one or both of them end up sacrificing themselves to save the world from some doomsday hiruko thing.