Two correct sentences are: 1. You are better than her. 2. You are better than she is. You cannot say: 3. You are better than she.

Normally we say ' you're better than her ' . Use the object form her/him/them/me/us . But in formal, we can use subject + be . ex : You're better than I am.

I recommend using "You are better than she is" because it is correct grammar and will also sound natural in casual conversation. "You are better than she" is also correct grammar, but may sound too formal in casual conversation. Some people may think you are saying it wrong (since they more often hear the incorrect "You are better than her"). Other people may think that you worry too much about trying to sound smart with perfect grammar. It is not grammatically correct to say, "You are better than her." This is, however, how many Americans will say it. So, it is fine to say this in casual conversation, but not in formal writing for school or work or in conversations where you wish to impress the other person (like a job interview). For someone who is just learning English, I think it is safest to include the verb at the end of such comparisons ("She is taller than he is") because this will sound correct to everyone who is listening to you or reading what you have written.