The answer is...
1st Appearance: Marvel Two-In-One #88
Last Appearance: Avengers #222 (coincidentally, my first Avengers comic)
Some scenes of the car from Avengers #221 and 222 can be seen here.
And the fate of her car?
She gained the Cadillac as a payment for doing commercials for a used car dealer in MTIO #88.
After she cut Hawkeye's cab off (before they met), he took an arrow to the car in a fit of road rage, shorting out the electrical system. (#221)
The next issue, she was seen trying to fix the car. Getting frustrated, she pounds the car into scrap and tosses it in (or rather, on) a trash can.
"There's magic in the sound of analog audio." - CNET.
I reread the issue; whether Wonder Man actually joined in his first outing is highly ambiguous. I don't think anyone could win an objective argument over it, so I'd say go with that's supported in the title, that shows Wonder Man actually joining after his resurrection.