That's so nice that your cousin invited Mabel to the party! Sounds like she had a great time and of course, got lots of attention
The incident with the other dogs...entirely the fault of the person who allowed her in the room where the dogs were. Why would he think you were "kidding" about such a thing?! must not have experience/knowledge about dogs, i'm guessing(?) In any case, sounded like a fun time with a little excitement thrown in there too!