I think you're right that you shouldn't take it too personally, that everything will be taken the wrong way. It's part of human nature when there is mistrust.
I will say that your text message was a bit curt. In fact, I read your first line, then the text message, so I thought it was hers for a second and felt you had reasons to be upset. Perhaps this:
"I'm sorry, I can't meet up prior to 5:15 because of work. Also, I'd like to find a nicer place than parking lots. Perhaps [park X nearby]? Thanks"
I'm not sure why you don't like the parking lots, but the text could be adapted to your reasons. Also, notice that my reply makes it less work for her, if she goes for the suggested place.
I know how tense the communications are with your W. I'm not going through anything similar as mine seems keen to engage beyond what I offer. I'm just saying that given that she seems offended by everything you say, there might be some social lubricant to help eventually.
I know you don't mean to, but be very careful not to appear to put the daycare staff in between you and your W. I think calling them to apologize on behalf of your W was just that. Your W did the same when she said you're being difficult. You're fighting for their sympathy. Right now, it plays in your favor, but soon it could turn against you because either the staff will become uncomfortable or your W will realize that they are on your side. Keep playing cool and they will just see.
M39 D6 D3 (at S) S 2014-09 D 2016-09
"You can't start a fire sitting around, crying over a broken heart" - Bruce Springsteen.