Thanks for the replies everyone. It seems the majority consensus is that I overstepped in my second email. I have not pressed (and will not press) the matter further. I respect Carrie's decision to never leave before 5pm. I guess I was just taken aback at her stance, given our workplace has such a great reputation for flexibility - I have never, ever, heard of any manager instructing an employee to always work between 9am-5pm. But that's no excuse for me overstepping - I accept that now.
And yes, in the past, there have been several instances where Carrie has asked for a concession (in her favour) and I've done my best to be flexible. Off the top of my head, I can think of the following examples:
1. The beer example. I agreed to change it to coffee instead, because I figured friendship is more important that drinking the beverage of my choice;
2. I was giving a dinner party, which started at 7pm. Carrie rang me that morning, and asked if she could come early at 6pm, because "she'd be in the neighbourhood then". This was pretty inconenient for me, but I made it work, because Carrie is my friend, and it suited her better to arrive at 6pm.
3. Carrie invited 5 of her best friends (including myself) to her birthday party, which started at 7.30pm. The day before, she contacted us, asking us if we could come for afternoon tea instead at 3pm, as she'd been invited to another party that night. Again, I (and the other guests) agreed to that change.
Yet on the rare occasions where I ask for a concession that would convenience me better (eg "Can we meet for lunch at 12.30, rather than 12.45pm?") Carrie usually finds some reason why it's absolutely not possible. I think in future, I will be a little less flexible myself.