Not too impressed by the non-inviting SO's. But, she got one detail right - she only invited people to the shower who were invited to the wedding. I do feel she should not have set up her own potluck to celebrate herself, and the invite to the shower should have come from the hostess, not her.
The question is probably how much pressure your partner is feeling to give her gifts or attend her events. I can see a gregarious boss thinking, "come have fun," and I can see another thinking, "gifts." One is thinking of you, the other of herself.