I would recommend going one step beyond however far you think you should go and see what happens. At the very least I would've walked her to her car and did a little makeout and got her #. Especially, since you mention she's older, I would've called to make sure she made it home OK unless my gut told me she's had lots of problems with overly needy men. You can also have a friend come "pull you away", then come back later. Sometimes if you traded numbers as the friend pulled you away, the girl will even text you asking you to please come back.
If the girl seems flaky and you think you won't hear from her again, then I would recommend just closing the deal right then. There's no one way I've seen this happen. Often cave manning her ass will get her to suggest you two leave together or you can suggest it. Sometimes saying let's go get food works if she seems reserved about leaving with a guy. Sometimes it just isn't in the cards. Simply saying you've had a few drinks and want her to drop you off at your car the next day is good enough for the car issue. Unless you're in NYC, I would try to get something soon. Having a car is pretty handy.