Yes she should be tearing the sack but if not you should help her by gently breaking it open and pulling it past the kittens head so it can breathe. What color is the kitten?
Pick the kitten up in a towel and rub her pretty aggressively but not to hard....this will stimulate her to breathe.
If she is still not responding...cup her in your hands (wrapped in a towel) and swing her between your legs once or twice....this will get the flud out of her lungs.
She could also not respond because she was in the birth canal for a long time.
Stimulate by rubbing the body with the towel especially the along the spine vigorously with the towel, if breathing does not begin promptly, aspirate again, pull on the tongue, & stimulate with rubbing again. IF the kitten doesn't start breathing promptly, put one (1) drop of DOPRAM under the kitten's tongue - do NOT repeat. Then begin stimulating by rubbing again. Keep up all stimulation efforts (rubbing, aspirating, pulling tongue) for five minutes or until the kitten is breathing properly.
If there are wet sounds in the throat or chest despite aspiration, hold the kitten in both hands with the head of the kitten pointing toward youor finger tips. Raise the kitten above your head & then swing the kitten down in an arc in front of you explosively (suddenly & rapidly) several times and then aspirate the kitten's throat again. This should cause any fluids in the trachea to move into the throat where you can aspirate them.
Warmth
Once breathing regularly without gurgly sounds, the kitten should be placed on a heating pad. Then clamp the cord slightly closer to the body than the original tear, clip the torn end, apply iodine to the WHOLE cord and around the base, and remove the hemostat, reapplying iodine to the area that had been clamped by the hemostat.
I advise letting the mother sniff & wash the kitten if she is not in the midst of delivering a second kitten, then returning the kitten to the heating pad until all the kittens have been delivered.
How's the kitten doing? Is it breathing? Responsive? Oh, I do hope it's okay, and that momma is too! I'll say a prayer for your little guy/gal! All the advice given above is great advice! That's the best you can do!