Well, my understanding is that, if you will have a friend visiting during an event, you decline and let them know that you have a friend visiting. It's not passive-aggressive, assuming that you are behaving correctly. Behaving correctly means that you are RSVPing no, and giving them the reason, and that you understand that that's the correct thing to do because you cannot invite a guest to somebody else's event. What the hostess *may* choose to do, then, is to extent the invite to your guest, thus enabling you to come. However, whether she wishes to do this is completely up to her, and it is not a social requirement. Anna and her guest were rude to complain about it to Anna's sibling, and her sibling was rude to complain about it to the birthday girl's sibling, because it is not a social requirement to invite an extra guest.
Anna was also rude for RSVPing yes and then forgetting the party. I'll give everyone a bit of a pass here because of the major national tragedy, but in general, forgetting the invitation and inviting somebody over instead? Rude. And then expecting that your guest should be invited over? Man, and *she's* the one who complains?
I'll give the birthday girl a pass, because a) she was young enough not to understand that she had the option of inviting the extra guest, and b) it's not a social requirement to do so regardless.