black wedding guest dress

If anyone can help me please let me know. Tim Tebow sponsors a Night to Shine prom for people with special needs. This year it is Friday, February 9, 2018. We just found and I am needing to find, buy or borrow a prom dress, size 14//16 for my little sister. If you know of anyone that can help me please let me know. My sister went last year and it was the best time and she was so happy. If you know who sells prom dresses I will buy one if I have to. Thank you for your help. You can message me if needed. Mary black wedding guest dress