you have to get lucky, sorry kid
Answer
Don't offer anything but love and you will find out really quickly.
You know if someone loves you if you can trust them impeccably when they are out of your sight.
affection
As this someone will always like to call you and talk with you. The body language and the eyes can tell everything that someone loves you.
you go to her house. meet her , tell her he loves you and she needs to find someone else
If someone loves you, they'll stutter or hesitate when they talk to you, they'll be protective of you, and they'd probably have a flirty look in their eyes
talk to Them
If someone loves you all they want to do is be around you and talk to you constantly. They will do anything to make you happy.
No she wasn't. She loves to sing and loves to know that someone cares about her. She is very, very happy.
if someone loves you then they would look at you or smile at you all the time. they would also tell you something he or she never told anyone like if the love you.
Answer You know if someone loves you back by their body rythem, the way they look into your eyes should tell you but if your really don't know, why not ask that person, that way you won't have to guess, you will know.
just tell them
Your question is contradictory. "What if you love someone and she loves you back but she doesn't?" ...Clearly the answer would be that she doesn't really love you, and you know this, as you stated "but she doesn't."