I wish/hope my friends understand that when I turn down a party, or leave early, or look like I am not having a good time because I am quiet or by myself for a few moments, that it has nothing to do with them, or the party. I am probably having a good time, or have had a good time, and I definitely appreciate the invite. It's just that I am probably totally exhausted by the people. Or I just don't have it in me to venture into a room full of people I may or may not know and small talk. It's scary and exhausting. At the same time, please don't think I want you to stop inviting me. Please invite me. I want to be a part of things..I just may not want to be a part of everything.
I would love to go to lunch or coffee or dinner or a drink with you and maybe on or two others. I would talk and laugh and have a wonderful time, because you see, I can handle a small crowd in a manageable setting. So have some grace and understanding with this introvert when she doesn't show up or seems less than enthused after a few minutes at a party. She loves you. Then, offer her a cup of coffee and a little one on one.