Oh dear, Sneaky, that's tricky about Sue. Perhaps the angle you could take with anyone who questions (and TBH I doubt anyone will!) is that your DD won't take anything but boob. It was true for my bf baby and for many others (even if you haven't tried, you have no idea, so you can't leave her to perhaps be very hungry).
We had a kid-free wedding too, except for our nieces. I know we offended loads of people - they did see it as a massive inconvenience (because our wedding was an hour away from Sydney up in the Blue Mountains) but the venue just wasn't big enough or suitable for children. There were heaps of tables squished into a small space and some quite steep stairs.
I was pretty young and more clueless than most people when we got married, so for the most part I didn't take other peoples' feelings into account. If I were older, I would possibly have suggested we hold the reception somewhere more child-friendly, given we were asking people to travel so far from home. Babies would've been welcome - I think it is only when they start to toddle and are in danger of hurting themselves and the things around them (potentially very expensive decorations!) that people suggest kids stay at home.