When a woman says "You always know how to make me smile," she's flirting. Melannie Gregersen explains this as her admitting you make her happy and she enjoys your company. It's a casual compliment that's easy to miss but signals real attraction.
The next phrase that she's secretly flirting with you is, "You always know how to make me smile," or, "I always feel like smiling when I'm around you." Something like that. When you are admitting to the other person that they make you smile, that's a big deal. It means that there's something about you that makes her feel good, that makes her feel happy. She enjoys being with you. She enjoys her time with you. So this is another one that could be easy to just kind of not even notice because it can be said so casually. But pay attention to that. This is definitely her flirting with you. She's trying to express in her feminine way that she's attracted to you, that she's interested in you, that she loves being with you.
