Again, that someone called the venue doesn't seem like a big deal to me, just someone who wants to hear it from the horse's mouth, so to speak. As it is a public venue, even if it is owned by your friend, shouldn't be such a crime. Some people would, some people wouldn't.
How would it be relevant to OP's guests if the venue owner said the dog rule wasn't a venue rule? The OP is hosting the event, and the OP reserved the venue for that event. The OP said "No dogs," so dogs are not allowed at the event, whether or not the venue would allow them at other times.
It's relevant because that's the situation--the OP said it was the venue's rule. They know it's the venue's rule. They're not calling the venue to go around the OPs rule, they're double checking to make sure that it is the venue's rule, that the rule is in effect and hasn't changed. What I don't understand is why she isn't just letting it be at that?
As I said, if it were a rule set by the OP, then they would be boundary testing her.
Look, I'm not excusing people for testing boundaries. It's one of the most annoying aspects of dealing with people whether you work for a venue, a church, or are just having party in your home.
And I'm not excusing them for not simply trusting their host, but such is the deal when dealing with family, sadly.
I just don't think the OP should turn it into more drama when it's literally not her problem.
For instance, if it were the OPs rule, she would have to take steps to make sure it was followed. But, that's not the case. She doesn't have to do that. Even if people called the venue and said "the venue allows it" the response would be "but I don't." But that's not the situation.
And while I can understand her maybe not wanting to pass that burden on to the venue owner because she's a friend, the venue owner is in the best position overall to handle the situation without drama.
I feel that the OP is creating drama from a situation where it's not necessary. People are gonna people.
If she is insulted or annoyed that someone didn't trust her, that's another issue. But, honestly, I think the OP can just relax and let the cards fall.
She certainly doesn't have to provide any kind of accommodation for pets.
And seriously, it might mean that someone brings their pet, is denied entry, has nowhere to keep her pet and has to leave the party and not come back.
It can be uncomfortable to just let that happen, but letting it happen, ensuring a consequence, is the best way to make sure similar things don't happen in the future.