Not sure if this counts as a "flaw" that was being referenced, but if I had to say from my experience it would be in her personality, not looks. It's not something that should steer anyone away, but I think Momo's an extremely shrewd girl. If you suspend your disbelief, you can see the act she's putting on, the compliments, calculated questions - she's masterful at creating the atmosphere you would want while seeing a girl of her caliber. Would I consider that a flaw? Not necessarily, but if you think you have a genuine connection with her and then notice this, it can disrupt the perfect fantasy you've been living in for that one hour.