Confused in love

My closest female friend from University, she has a childhood best friend. I know her and spoke with her once in a while just random jokes on Instagram.

Last month I was talking to her and she said we should meet and I went to her university where she works as a lecturer. From 1pm-5pm we spent time with each other.

When talking she told me how a person she had feelings for left her saying he only thought she was his friend. It devastated her. But during the conversation I was genuinely impressed with her qualities and felt that I'd be great if we were together.

My best friend (the girl's childhood friend) said I can try but told me there are alot of constraints.

Once I called the girl and we spoke for 3 hours and had a great conversation.

I'm leaving for the UK in a few days. Today, I was supposed treat all my friends for a farewell lunch. But unfortunately due to circumstances it had to be cancelled.

Later, I only invited my best friend and the girl. After that when they came my best friend brought me a gift. After an hour the girl I like arrived. And she brought me a farewell gift too. To my surprise, her gift was very considerate. She picked things which she believed I'd like and it was beautiful.

I had written a letter for the girl. I did it because I wanted share my feelings without burdening her with any kind of emotional turmoil.

I told my friend to give it to her after I left. After an hour my friend told me she gave her the letter.

Now the girl didn't pick up my friend's call. Should I be concerned? What do you think is going on in the girl's mind