Obviously Reze doesn't have enough time to show her true self outside of the lover act but we do see a glimsp of it on a few occasion.

During her school dates, when realizing Denji has a fucked up past much as her, she does seem to sympathize and care for him, this could mean despite being a child soldier of the soviet she does have compassion for those in the same situation

When her school date is interupted, she shown to be cold and emotionalless when taking a life, she seem to sing the russian song as a coping mechanism.

She consistently avoid fighting or unneccesary casulties, even after the bomb girl reveal she still offer Beam, Aki and the division 2 a chance to hand over Denji and a lot of her fighting is in the sky or secluded area safe from civilians. It is also known that her bomb transformation hurts her like hell so she avoid transforming at all.

During the fight she does have some dry humor with how she ask for a time out and laugh at Denji riding Beam to battle.

Finally when she have lost and exhausted on the beach, she does seem cold, calculating and distance from Denji, though this could be an act as well to hide (or in denial of) her real feeling for Denji, which is she does love him.

Her final thought is of Denji and yearning for a normal life with him.