"How do I make her feel like I'm NOT treating her like a child?"
By watching your tone. Talk to her like your equal.
"I'll stop telling her I had a good day, goodnight will be enough. I'll just say "thanks" when she does something nice."
Why? You don't need to be a d*ck. Just watch what you say.
"The being treated like a child issue seems to be stemming a lot from the use of the car"
No I can tell it's probably how you talked about other things as well.
"she's so in those mode of "I don't have to report to you" that she doesn't share much info with me until the last min,"
Then talk to her about it. Just tell her that you would appreciate it if she could tell you things ahead of time so that she or you are not inconvenienced.
"If I take the car away I'm going to get the "I knew you'd do this, you're a dick and don't care about me or the kids"."
Mindreading. And in any event, this latest issue of the car would've been handled better if you would have told her instead (after she says what she was going to do)..."that's a great idea. Either that or we could (your suggestion), which would shave off time from your commute. What do you think?"
That's how you talk. You validate what she says (DB skill), offer your suggestion and ask for her opinion so that it doesn't seem like you're just wanting to do what YOU want to do.
Get it?
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.