Unless you're a 13 year-old girl, you're gonna need a stronger grip than a 13 year-old girl. Jiu Jitsu and grappling in general, as a martial art and sport, demands that the practitioner or athlete (whatever you prefer being called) maintains a certain amount of useful grip strength. I'd even take it a step further and say, you can never have too strong a grip. It just goes hand-in-hand with the practice of submission grappling (pun very much intended).
On the flip side, if you will, over reliance on one's hefty grip can also be a grappler's downfall and is definitely detrimental to progress. It's pretty obvious, but I'll spell it out: many a time, a grappler will compensate for his or her weaknesses in other aspects of grappling (e.g., skill, flexibility, speed, strength, endurance, cunning, gameplan) by relying solely on his (or her) bountiful god given vice grip. Not good. I see this most often in the more junior ranks. Avoid this, but at the same time, make sure your grip is strong enough to be there for you when you need it.
You can develop a strong BJJ/grappling-based grip, I believe, purely from training BJJ and grappling. But, if you want to impress the ladies (or dudes) by ripping some poor schmuck's brand new Black Star sleeve clear off at next year's Pans, you're gonna need some special training. That's where friend of the DSTRYR/SG family, Adam Glass comes in. Adam is a practitioner and coach in the area of seriously hardcore and very practical strength training. He's also a certified grip champion and overall badass at crushing things with his hands. If you want to acquire a grip like his, you might want to check out his DVD series, Industrial Strength Grip (Vol 2). Or, maybe you just want to watch a few vids (below) and glean a bit off that. So, do it.
BEHIND THE BACK WRIST CURLS
PINCH GRIP DRILLS