Single daughter being left out of family - how to bridge the gap?

My husband and I have one daughter, Jane (not her real name). She's 26, has graduated college, and has lived on her own for years. She's not any kind of criminal and is not that much younger than her cousins. She's single, and while she dates a lot, none of her relationships last very long.Of my husband's 4 siblings, all have multiple kids and all of them have been married at least once before and have kids. They're all very close because they all do couples and family centered events. While she's always tried to form relationships with her cousins, Jane isn't invited to these things because she's a "spinster" and "wouldn't relate".My daughter Jane has been sad about feeling left out of the family for years and while it was harder to see before, it's clear as day now. We thought it might get better when they were all older, but it's only gotten worse.One of my nephews is getting remarried, and Jane wasn't even invited to the wedding until his mother admonished him to send a separate invitation. He said that it was implied that she was invited under our invite. Jane doesn't live in this household, and being unmarried doesn't make her a child.It hurts to see that Jane doesn't really have an extended family, and won't have any relatives after we're gone. Is there anything we can do to bridge this gap? via /r/Parenting http://bit.ly/2JxPMGw