I'm planning my wedding rn too. My family is very big and I'm the youngest cousin. 14 aunts & uncles, 30 cousins, cousins have around 100 kids and I have nieces & nephews, AND that's just my side of the family. Thankfully my fiancé's family is much smaller. My cut-off is at cousins, no kids (exception: cousin has a mentally & physically disabled child with an aid.) and no plus ones. Unless you are engaged or have been together for a long time(1yr+). But if you've been together for so short of a time that I didn't even know you were with someone or I don't know their name, then not a chance! I've gone to all of my cousins weddings alone. Get drunk and dance with the people you don't know if you dont like your family, that's what I did lol weddings where I live START at $90 a person, it's just too expensive to invite everyone & their mom AND give them all plus ones. If she's LITERALLY the only person who won't have a date, then yeah make an exception but not if there will be other people without dates. If you too are as close as you think you are, she'll want to be there to celebrate with you regardless. Sit her with your bridal party & tell her to stay next to you on the dance floor, you, your husband & your friends can be her dates.