Most likely, they chipped when she fell. She doesn't even have to fall very hard for that, because they likely chip because they hit against the tooth on the other side.
Small chips are not a problem, I think, because they affect only the outer layer of the tooth (the enamel). And the chips get smooth from "daily wear," so that's also a normal process.
As far as I know, fluoride is a very good strengthener for teeth, and smilemomma always recommends brushing the teeth with a good fluoride toothpaste such as Tom's of Maine.
Oh, another thing: do you remember how friggin sharp
those first teeth were? The edge is very thin (that's why I called my dd Ms. Razormouth for a while
), and it also wears with time. Are the chips just in those edges? That wouldn't even indicate a fall, they would just be wearing smooth. In that case the chips would be teeny tiny.
But either way, as long as they only happen at the edges, I don't think you have to worry too much. Keep checking the edge though, so you will see the discoloration that would go with decay if that happens.