My girlfriend it`s always in a depression.What can i do to help her?

Well, sometimes its unavoidable that we feel depressed for the day..but for the health its not a good side, i believe in Meditation which will balance our mind and helps to be normal at situations

Try to keep her smile on her lips.. and try to talk with her much from now on.. and I think will be better! :)

There is a difference between a Girlfriend and a lover.You have used the word "Girlfriend".If you have meant that she is your lover then may be she is feeling insecured with your relationship or may have some previous bad experiences,the best person to help you is a professional pchycologist who can try to remove her mental/pschycological blocks by counciling.