I don't know about the birth itself, but afterwards, she will likely need high protein food (canned if you aren't already feeding her that.) as much as she wants. Also, try to switch the kittens to solid food as soon as possible to take the demand of being the sole food producer off Mom as soon as possible.
Dr. Seuss~DLH (brother's cat)~June 2007-
Misty~DSH (my cat & Mooby's mom)-?-
MooBoots(Mooby) ~ DMH(Mom's cat)~July 21, 2008-
Sunshine~ Golden retriever X white german sheperd (Dad's dog)~October 24, 2008-