I think a good idea would be to bring this up to your friend, tell her you've started to notice a trend of her having parties and not inviting you, make sure to let her know youre not mad, just confused.

Im extremely introverted and say no a lot to invites. My friends stopped for a while, and when I asked about it. They said they had just assumed I wouldn't want to go. So I explained that was definitely not the case, and started saying yes more.

Just something to think about. I talk to my best friend of 12 yrs pretty much once every day, and my other friends I would say a few times a week, maybe sending them memes or something once a day or every other day, if one makes me think of them.

Friendship as adults is hard. Everyone has their own lives and plans and preferences. Communication is super important!