So here’s a first: we’ve had a superhero same sex wedding before (the wedding of Northstar and his boyfriend in Astonishing X-Men #51), but I don’t think we’ve ever had a superhero officiate a same sex wedding before. So perhaps Wonder Woman is the first. (Or am I forgetting anything?)
The wedding was during Sensation Comics #48, a digital comic that came out 8/20/15. After Wonder Woman stops the invasion of an Eastern European country, she comes back to New York to officiate a wedding:
Heh. I like how Diana has to point out to Clark that Themyscira is made up of all women, so she is completely fine with same sex relationships (a fact was I believe was also pointed out during Gail Simone’s run).
In any case, here’s the cover to Sensation Comics #48, which is also pretty awesome: