Not so sweet sixteen

My youngest daughter is turning 16 on Saturday, and almost ready to pass her behind the wheel driving test. Appointment is set up for December 31...I know, got to squeeze it in there. Have to have it before the end of the year. Well, in her mind anyways.
So we thought we had worked out a deal with a car. My oldest daughter just bought a new car, and was nice enough to gift her 2002 Ford Taurus to the 16 year old. Well, the car needs $1,700-$1,900 worth of repair. I specifically told my youngest that if we're going to help her out with this car she has to ask her dad to help out with the repairs too. I told her that she needed to tell him that's what she wants for her birthday. I just had my car fixed for $622 and christmas is around the corner. I am not going to do it all. She said, "but mom, I can do it. I'll pay you back", Well, this kid does not have a job, and has not done much trying to find one. I got her a baby sitting job, but half of the time she is asked to baby sit she has other plans. So, there you go. "Well, I have my allowance!" was her reply.
I made it very clear to my daughter that I really needed her dad to help out if this deal was going to take place. I told her to call her dad and explain the situation. This car is way below blue book value and once it is fixed it will easily sell for $3,000. So, I figured her dad would see this, and realize if we wait until next summer getting her a car will be a lot more expensive. I even sent her dad an email giving him a heads up. He didn't get it unfortunately. Instead he calls my daughter up and asks what she wants for her birthday, and she briefly tells him about the car. He says "I don't think you really need a car. How about a laptop?" The girl freaked. Of course she wanted a laptop. She wants it all. So, the idea of getting her dad to pay for half of the repair flew out the window. Instead she calls me all excited, "I will babysit a lot. I can still get the car and pay you back."
I told her that it wasn't the deal we made, and that she is going to have to choose. I am not paying for all the repairs. I will let the car go. Now, I am the evil mom who ruined her birthday. I called her dad and asked him to reconsider. Not only because of the car, but also due to the fact that I have already bought my daughter a laptop. It's her christmas present. It was supposed to be a huge surprise. I bought it a month ago, so that I would have time to personalize it. I had already envisioned her and her sister's shrieks of joy when opening their presents. My exhusband asks, "Can you return it?"
My daughter lives with me 100%, so I feel that I really know what she needs. God forbid he should have called and asked me about what she could possibly need for her birthday. Why didn't he realize that maybe I had already bought her a laptop. But no, he goes ahead and promises her a laptop without discussing it with me. So, I am screwed either way. I am big on principles, so I will not let this one slide. If she wants the car bad enough she has to follow through with the original plan. Her dad said he would pay for half the repairs, but is afraid that our daughter would be very upset with him if he doesn't keep his promise about the laptop. So, we're both screwed. Either way she will be upset. I do not look forward to this coming Saturday. And to add to my frustration she invited her dad (did I mention we don't get along) to her birthday dinner which I'm cooking...arrggghh.