It's the OP.
Wow, this has blown up and appears to be quite divisive with strong and opposing views and a lot of nastiness.
To add context, we didn't even register there were two pads when we walked in and locked the door automatically. When I realised there were two I assumed they were for different aged children and we used the smaller one. We saw two other mums and babies go in later in the day and they both locked the door too. We definitely didn't do anything unusual or wrong.
I wasn't asking for people's opinions on both of us changing the nappy. It's nobody's business and the only impact it has on anyone else is a positive one, because of course it's easier and quicker with two pairs of hands and the space will be available sooner. We enjoy both being involved and will continue to do it together when out in public regardless of how old she is.
But one of the people commenting clearly didn't read the post and told me I should have gone in too to help my wife lol so I guess it's a case of damned if you do, damned if you don't.
Someone else said I should have answered back to the woman and defended my wife. I did. But as we were both changing the nappy, I was defending both of us.
To the people saying we should have used the ones nearby - we didn't know there were other changing facilities nearby at the time and still don't know whether they only had one pad or multiple. We had never been there before and had only just arrived.
And to the people expressing concern over my wife's anxiety - yes, she is getting help.
After this happened, we checked with a staff member whether we're allowed to lock the door, and they said of course, it's up to you whether you want privacy.
So, to sum up, if we were to return we would definitely lock the door again.
Anyway, I'm going to forget about this and move on with my life now. Thank you to everyone who answered with kindness.