To me, the relevant part is: “and now doesn't want to be friends with Kate anymore because of the way Kate acted at the wedding.”

No matter how it went down, once post-wedding and Bride is clearly informed that Kate’s dad was dying, I don’t know how she couldn’t say that Kate had reason to be moody—and even managed to pull it together!

I get Bride being absolutely snowed under with planning ahead of time. I get, as Carolyn says, Kate sounding like she’s kind of a pill usually. But cutting her off because her behavior at the (beginning of the) wedding day sounds off, and worth questioning.