My opinion…
There is not enough information to go on. Nowhere in the mother’s post did she say that her daughter had social anxiety. That was suggested by a CC member. It is plausible, of course, but we don’t know that to be the case at all. The mother simply states that her daughter doesn’t like parties and didn’t really want a graduation party and reluctantly obliged. This could be a case where the kid didn’t want a big deal made over graduation or thought the party wasn’t cool, or friends were not having these, or doesn’t like to be center of attention, or any number of reasons, in addition to some social anxiety in such situations. One could say that the parents should not have held the party since their daughter didn’t really want it. But I don’t see it as terribly wrong that they had the party since it was rather a small gathering of relatives (some may have been from out of town attending the graduation) and some close friends. They wanted to mark this milestone and were not solely doing so for their daughter since she didn’t even want it. But I don’t see it as far fetched that they still had a gathering.
Then, unless this teen has severe social anxiety, I think it is reasonable she should have to attend the family gathering. Sometimes people, especially minors, have to do things they don’t really want to do, just to appease their parents. Does this daughter attend Thanksgiving family gatherings, holiday gatherings her family may host and so on? Was it just that she was against a party for this occasion or anything that centered on herself? If she has a severe social anxiety, I would think the parent may have included that in the post, but who knows. If it is indeed that severe that she could not hang out at home during this gathering, I wonder how she handled the graduation event itself or will handle college situations? In any case, there is not enough to go on as to why she didn’t want the party except that she “hates” parties.
Meanwhile, I do think the situation was awkward for the parents. And I think what is really not OK is that the daughter did not acknowledge her own grandparents for coming for this occasion. Unless she has some severe mental illness issue, this would not be acceptable in my book.
In terms of thank you notes, I don’t understand the mother saying the daughter won’t write them. That is not acceptable, regardless of her attending or not attending the party. When gifts are received, thank you notes are to be expected. My kids had to write them. There is not a choice with this. I think she should have to write them or else some consequence is necessary…this might be returning gifts if not willing to thank people, or loss of privileges or some such. The gift and thank you notes is separate (in my view) from whether they held a party or not or whether she attended or not. It would be a long held expectation. I think the daughter should apologize to her grandparents too as in my opinion, her snub of their visit is not OK and not even that related to the party itself.
Again, not enough information, but I would not assume a severe social anxiety without any information provided, though it is a possibility, but just one of many.