Glad you're going to talk with the bride, Rock17! That way you can't "go wrong."
Grannypiper, true the MOB is 'not the Carnival Queen," LOL! But wedding etiquette says that she's supposed to take the lead, as a PP mentioned. So, personally, I wouldn't wear a hat if she weren't or at least, not a very big one. But if Rock realy wants to, it's best if she checks with the MOB or the bride first, IMO. As you can see, she's checking w/ the bride.
Oh Greyduster, what an awful situation! And how rude and ridiculous for the MOB to act that way! It's not as if you did it on purpose!
Annie, I don't think that dress is "too posh." It is lovely for "afternoon tea," IMO. Please go ahead and get it! But Riverwalk's comment about length has made me think - just be careful that you get the right length for you.