Flaky Sister

My wedding is in 25 days. My sister doesn't have a plane ticket yet. She hasn't even started to set aside money for a plane ticket yet. She's known the wedding date since last February. She has always been really flaky in general and irresponsible with money. We're only having a FG, so it's not like I've loaded her down with typical BM expenses. I even have a place for her to stay for free. She just needs to get here. We're already pushing our wedding budget to the max and can't afford to be buying plane tickets for her and her daughter. I say that it's time for her to accept reality. She always has to be the victim. Somehow it's my fault that she hasn't saved any money. I've been really patient and only asked her about it once. I really need to work on my seating chart, and I need to give the caterer a final number this afternoon. Too many big things are hinging on my flaky sister. Also, she never returned her RSVP because she loses EVERYTHING. Ack! My FH and I both have family far away. We knew not everyone would be able to come. We've been at peace with it for awhile. Am I horrible for wanting to finalize my planning?