If she would do anything just to see you happy or if she would do anything, even lay down her life for you. If she puts you before herself. If she is committed enough that she wants to spend the rest of her life with you. that is love. The better question to be asking yourself is do you love her.
You can tell if your girlfriend loves you by the way she treats or talks to you. If she seems uneasy around you, the feeling may be fading. If she is excited to see you and responds to you favorably, she is into you.