Is she small for her age or just too young? Is that why you are concerned about having to help her birth them? Usually the mom cat knows how to give birth, and what you need to be aware of is that sometimes, the female will sit on her kittens and smother them. You just need to be there and move them out of the way once the sac is broken and the kitten is licked clean.
If the cat is really young, there is a possibility of many problems and you will want to call a vet and get his ideas and suggestions. Good luck!
I moved this to the health forum so it would get noticed. You should do a search on the site for some more tips. There have been a few discussions on this over the past months. What Hissy said is true, most cats have that natural instinct.