I don't want to go to a friend's wedding after she hasn't attempted to make any contact with me for months
Is it because she's ignored you for months?
That's one of the reason yes.
It hurts to be ghosted for months at a time. But, if you RSVP'd for the wedding and your friend expects you to show up, you should go. I'm sure they were just super busy with wedding planning and that's why they haven't been in contact much. They still clearly want to be friends if they invited you to their wedding!
I can just watch the wedding online so I don't have to go.
I really think you should show up in person. Attending the wedding would give you a good chance to catch up with them and to show them that you support them! Now that their wedding planning is over, they will have more free time to see friends.