Am I overreacting?

Hii, Im Julie :) 

(Sorry for some writting mistake, English is not my first language)

Im the kind of people that wants to get along w everyone, Im always doing my best to be kind w everyone and to include them, I know that Im not perfect and I try to understand when im wrong.

I have a group of friends,  there are 11 of us and we get along well with each other.

Last year, on February, one of the members of the group was having a birthday, and thats okay, but in june I discovered that she made a party. In that party it was eveyone of the group, except me. I found out that she created a group chat on whatsapp w every person of the group, but didn't add me. I got sad bcs nobody told me abt that party that i wasn't invited, i just found out bcs they shared the pictures in our usual group. Im always thinking abt this bcs it seems like she made it on purpose, bcs the only people invited were the people of our group ://

In December, we made a secret friend game and I got her, I gave her a colouring book (we are arts students and it was in her wishlist) and her favourite type of Tea.

Today I received a notification that she added me in a group chat, the same group chat she created last year, but now w me and another new friend, who was greeted by the old members when she entered the chat. The mensage "time to revive the group" apeared in my screen and I just wanted to cry. Do she only remember me bcs i gave her a present? Why did nobody noticed that I wast there initially? Am I overreacting? Be honest pls