I have more money than her. (than = preposition)
I have more money than she does. (than = conjunction)
However, if you read Shakespeare, or other noble writings, you might see:
I have more money than she. (than = conjunction)
It is grammatically correct, but then so is the other one (than her). You see, "than" can be considered a preposition here, and "her" always follows a preposition.