Is she rejecting you only in bed or is it a feeling you get from her behavior?

In order to get what you want you are going to need to put some effort in it. Show her it is not only sex you are looking for. Surprise her, cook for her , take her out for a picnic, take her back to the place were you once dated. Don't think negative, after these activities tell her you just want to hug her with no sex at all. It will surprise her but it will show her your intentions are true. Give her time till she will get the spark back and you two will enjoy it again. If its not helping at all and you still feel as if anything you do won't change her, then you will have to raise a discussion about it with her but only after you feel you have done anything you can.