First off, the rabbit she caught on the lamp, did you expect/want her to kill it also? Most pups do not kill their catches and its better they don't, thats your job..!
As for only giving her so many slips, it really don't matter how many, its the 'quality' of the slips that make the difference, because success is everything...!
Get her out often, go to the best places and give her the best slips and if your going well and catching, keep going a bit, you probably ain't gonna do the ton!