How did her behavior change?

Here are a couple graphs showing Jubilee's response curve.

Figure 1. This graph shows the average number of bar presses for each Fixed Ratio schedule. The number of responses increases as the amount of work it takes to get a reinforcement increases.

Figure 2. This graph shows the average amount of reinforcements received during each of the Fixed Ratio schedules. As the amount of lever presses required to receive a sugar pellet increases, the total amount received per training session decreases.