Teacher popping in to say that yes, there are plenty of kids who need a little more support in developing a tripod grasp. Part of the issue is that we're expecting kids to write earlier and earlier in our curriculum these days. If we waited to teach them to write they'd figure out the grasp on their own, but if they're using the wrong grasp a lot then it can become a habit that's hard to break.
The best way to "teach" a child how to hold a pencil is to give them implements that can't be held any other way -- tiny pieces of chalk and crayons, those "pipsqueak makers" that crayola makes, eye droppers (with little dishes of colored water to mix like a mad scientist!), little sponges for sponge painting, a saucer or shallow bowl with a very thin layer of glitter for her to pinch and sprinkle etc . . . All of these things naturally bring their fingers into the right position, or you can model the position when you show them how to use them and then the material will reinforce it by not working if they use their fist.
Another thing you can do to encourage it is to have your child work on a vertical surface, tape pieces of paper to the wall for her to draw on (I usually put a big brightly colored piece of construction paper up first and then put what they're working on on top of that so there's a clear stopping zone before they color on the wall, or buy an easel, or even tape paper to the bottom of the coffee table and have her drawing lying on her back like she's painting the Sistine chapel. That will force (force is a harsh word but I can't think of another way to say it) her to bend her wrist when she draws, and you can't really use your fist with your wrist bent.
Both of these things should feel like fun, if you feel like you're forcing her then I'd back off.