To learn the first limit within a level, you have to kill 80 enemies, and no, you don't have to kill them with the limit.

To learn the second limit within a level, you have to use the first limit within that level 6 or 8 times. I don't quite remember. I think it was 8.

To get her final one, you need to visit the guy who lives nearby Fort Condor in a cave.(need the buggy or tiny bronco to get there.) He tells you how many battles you've been in, and if the last two numbers are equal(466, 22, 144, and so on.), you'll get an item which you'll have to take to the house outside the desert where the Gold Saucer is. Pick the little box when asked what box you want.