What should I do?

So, me and Sarah (fake name) have been friends for 6 years now. We met in the 7th grade and became really close friends since then. Near the end of 10th grade we drifted apart as we didn’t really have a lot of time to talk and now we talk lesser but do still keep in touch from time to time.
Sarah’s birthday is in a few days and she’s having a huge sweet 16th birthday party and has invited half the batch.
My friends were all talking about it and I realised she hadn’t invited me, it really hurt me as I thought that we were close enough to be invited to each others parties, since she has always invited me ever since we became friends.
Let me preface my point by saying that she invited people she barely knows. She invited a friend of a friend, who told that friend, that she doesn’t even know Sarah and has no idea why she was invited.
I really wanted to confront her but I’m an introvert with a very non-confrontational ass so I couldn’t say anything.
Sarah probably just forgot inviting me and that pisses me off, because how the fuck do you forget to invite your friend of 7 years to a birthday party in which you have invited over 60 people out of which you barely know 20 people.
I don’t know how to go about this now. Please advice!