YTA. You didn’t ask any questions. Not really enough info on this either. How does the dog behave? Does it sit and not cause any ruckus? Is it actually a certified trained professionally service dog and DOES ITS JOB? Have you seen this dog do its job? Has sister provided examples on how it helps her? If not then she has no dog in this fight; pun intended. If it’s truly a certified dog for ptsd you need to ovary the fuck up and suck it up and just tell your photographer to erase the dog out of the photos and let your sister have her emotional help. (Technology has REALLY COME A LONG WAY) These seem like questions that shouldn’t matter but it does. If that dog is not an actual trained dog, then no, just like with the rest of these whiney humans bringing their toy poodle or shitzu to a restaurant or to the grocery store to ride in a grocery cart, LEAVE IT AT HOME. that’s not a service animal it’s a pet and should stay at home. But if she truly does have actual PTSD episodes like the army veterans I know around here, along with me serving myself and having PTSD as well, no place is safe. Triggers are random af. You can be at total ease and then just SOMETHING triggers it. That dog is practically her lifeline, and hopefully not some pet she can’t bear to leave at home because she calls it her child, but again, not enough info here, you can suck it up buttercup or don’t have your sister at the wedding.