What does my friend want from me?

I’m 19, she is 16. I met that girl online through a dating app. At the beginning I told her, that I’m interested only in relationship with her because I absolutely do not believe in Platonic friendship. She said “I need time to think”. I truly believed in my pick up skills and decided that I will be able to build a relationship with her despite anything.
We’ve been communicating for three months. She said that communication with me was longest and mentally closer than communication with guys before .The first month she blow off me several times but she wanted to support communication with me. Over time our communication became better and better. Fun walks, regularly texting all night, phone conversations until the morning. In the third month of our communication she began to tell me that she also likes me. She always said that she believes that there will be something between us, that I’m an ideal person for her and she is afraid of losing me. I offered her to start a relationship. She agreed. She said: I’ve already thought about everything and I do not change my mind. One the next day we went for a walk as usual. At the beginning everything was fine. When I walked her home she became more silent. I tried to kiss her for the first time. She dodged. When I came home I texted her on emotions that I can not communicate with her anymore, because I like her. She wished me luck. Three days later I texted her again and tried to return everything. She said that she doesn’t feel sad that I disappeared from her life. She said that she didn’t want to have relationship with me and that she didn’t want to communicate with me anymore.
This whole situation really motivated me. In a month of time I created great app for Google Play and App Store which raised my objective value at least in my eyes. I often thought about our relationship with her. I asked myself: is this really my fault? I remembered how many times I was humiliating for her, always tried to make her fun and to make her feel special. It should also be noted that she had 5 unsuccessful relationship’s before and during our communication she used an dating app. I finally realized that all these red flags were clear at the beginning.
Two weeks after we stopped our communication I accidentally met her on the street with her friend. She was in front of me, but looked around and saw me. All her body was showing how uncomfortable she was. God, it was a terrible actor game. I passed by and didn’t say anything. After that, she deleted all her likes under my Instagram posts.
It was my birthday a few days ago. Interestingly, that she wished me a lot of good things. It was strange to hear it from a person who said before that she doesn’t want to communicate with me anymore.I answered with a single “Thanks”. But the most interesting thing is that her best friend also wished me happy birthday, with whom I almost have never communicated before. She wrote a damn big text. I’m sure that they were together when her friend wrote me that message.
Now it has been almost two month after we stopped communicating. Every time I think that I have forgotten her, she somehow gives me something to know about herself. I absolutely don’t understand her behaviour. I don’t understand why she , first:
-truly believes in relationship with me, and on the next day changes her opinion.
-and why after we stopped our communication she congratulates me on my birthday and forced her best friend to do the same.
I’m so confused.