Sisters who quarrel

My best friend booked and paid for flights overseas for a week in Sep for me and two friends. My sister on the other hand wants to celebrate her 10year anniversary and renew her vows the same day I leave. Her actual anniversary is 3 days before hand. No time, date, invite or place has been set, only a brief conversation 2 months ago where she was said she was thinking of renewing her vows. Yesterday she asked me if I was available on her anniversary date, which I said I was. She then realised her anniversary didn’t fall on a weekend and told me she wants to have it the day I leave. I tried to change the flight to the next day but it will cost me another full fare (money which I don’t have). I’ve asked if she could celebrate it the weekend before I go or upon return but she won’t budge. Her reason is because it’s bad luck, I should have known and thats it’s her daughter birthday. I’ve also asked if she’s could help me pay for the flight so I could change it but she said nothing. She is now making me feel guilty and now now accusing me of choosing friends over family. Am I being unrealistic? Should I have considered this when nothing had been formally set. I don’t know what to do. I love my sister but she’s making me feel so bad.

Hey, I can see it from both sides. I think it depends if she knew you were going on holiday in September or not. And if you knew she was planning something then did you check with her if it was close to her wedding anniversary date. Maybe in that brief conversation she expected you to not plan anything around the time of her 10 th wedding anniversary and to keep some days or weekends free. And to make a mental note that she MIGHT be doing something. That’s why she said it in passing. But it’s not always easy to put your life on hold for others when they are being undecided. I dunno how long it takes to plan to renew your wedding vowels but I would of though it takes some organising? And tbh, if you really want close family and friends to be there, you do some organising and send out invites as soon as you can, so they don’t go on holiday or make other plans. September isn’t that far away. It sounds like she’s angry with you for even going away in this month. Er...I think that a no to her helping you with flights. Her nose it been put out of joint. Unless you pay her back over time? She’s probably thinking why should she. I think you’ve tried to compromise but a solution needs to be found. So I think talking to her calmly about this and try to sort out.