My brother's wife's niece (not blood-related to me)

My brother's wife's niece (not blood-related to me) I feel has a crush on me and I'm stsrting to feel the same. We have the same birthday and I caught her staring at me this past holiday season. She also picked the shot glass I drank from when we took another shot, and is playful towards me like she'd ask for a high five then starts dancing when I give my five. We see each other every family gathering and I feel we both are starting to feel the attraction to one another is getting stronger. How would you handle this? I have thoughts of inviting her over my place but her and I agreeinng to keep it a secret.