Trying to be a great Matron of Honor

My best friend, more like little sister, is getting married. She is having her Bachelorette party in Costa Rica and I am the only one who cant afford it. I am the Matron of Honor and I need to be there to support and make her weekend the best before her big day. I am mom of a 7 year old and 11 month old. All the money we make goes to all our bills to live. We have no extra money besides the necessities. The bride even paid for my dress until I can pay her back. She cant pay for my trip too. She begged me to go even though i have no money to pay. I have tried to make extra money but some bill is always showing up, like Dr bills for my sons walking pneumonia or moving expenses we had. Please any thing can help so I can be the best sister ever. Thank you.