Help

So i've been living in my appartement block for 5 years now. Last wednesday i was walking my dog and there was this girl i noticed straight away at the appartments garage. My dog walked straight over to here (good boi) and we started talking for a few mins. While talking i had this feeling i've know this girl even though i've never seen her before. The next day i was having a cigarette on my balcony (yes, bad habit) and she passee by on her bike and i kinda waved at her awkwardly but she waved back with a huge smile on her face. The day after i realised i've been friends with this girl on facebook when i was like 16 (im 28 now) and i've rememberd her name. I went a little joe goldberg on her and checked her facebook again and went to the main hall to check her name on the mailbox in our block. It was indeed this girl. So now a week went by and i still havent seen her again. What should i do? Wait untill i meet her randomly again? Go knocking on her door? Write a letter and put it in her mailbox?
I really would love to get to know this girl as she is a very nice and cute woman.