From what Maria said, he has always been kind so they must have been at least friends or have sense of partnership between them. And her personality shows that she had always been considerate of others, so she's not just suddenly gonna slap/pull away from the hand of her previous partner who had always held her hand in her past life (and seems to still haven't gotten over it). Rather, it's more in character to wait for a timing where she can smoothly tell him without offending him or letting Jou know (since she's hiding her feelings from him).