I'm assuming that this Momoko finds the faults of the younger Momohana to be very cute, especially in contrast to her talents as a maiko. Despite her deadpan face, she seems to be having fun playing the role of Momohana's elder (caring for and scolding her). She even seems to be able to read Momohana like a book (knew she was out of name cards, knew she actually wanted a cream soda). Thus, "love".
Well, that's my guess at least.