Ignoring my wishes: Bringing a plus one anyway

We are having a small wedding/reception due to financial reasons. Because if this, we are limiting the people we've invited to close friends and family. Ive had to tell some VERY close friends and family Ican't invite them. My five had had to do the same. My sister and I talked about this extensively months ago for the same reasons. I told her I'd if let her know if we can add another person IF someone cancelled. She sent little insinuating notes via our family text chat to which I reminded her of the same.

Today she let me know she and someone else are flying in a few days before the wedding. I reminded her about the conversation because I want to avoid drama.

She then said she feels "awkward" because they'd expect to come and that not coming would put their relationship in jeopardy. Oh.... and here's the kicker... she can't come if I don't let the other person come.

Im so frustrated because we are sooooooo overwhelmed financially. I already shared this with her but she's trying to guilt trip and manipulate me. Ive had to turn cousins down, my close prayer sisters, great friends, etc... down and they understood but she's pushing her way.


What should I do? Am I seeing this the wrong way?