The way I understood was base on my assumption and something that happened explicitly in the novel.
Remember guys there was another girl in that party, that spoke before sire appeared. She said something like "the reunion is under the protection of the Temple". I assume that "Temple" was the name to call the Camarilla here. It can be that or it can be another group that is not the camarilla.
If it is the Camarilla, clearly sire has nothing to do, as people would have known about her. Most likely she being the strong vampire she is, just decided to show up. The fact that her clan seems to not be any of the known clans and her characteristics are not known to at least all vampires we have known, she is not a known member of vamp society, but it is unlikely she have no way to let herself in, either but others letting her in or she getting in without others permissions.
If it is another group, it is more likely she had something to do with the arrangement, but the way she behaved and spoke game the feeling she was just there to enjoy the evening, and MC appearing was totally something that happened out of luck.
Only reason why I think this is important is for the future. I strongly don't think Sire cares at all about MC. I think she will eventually, but there was no underlying plot for MC becoming a vamp, nothing more than Sire toying with him out of boredom.