I feel sorry for you, but glad you have made this decision. If you feel better having made it then you have made the correct decision.
Sometimes horses are just too much for you and it takes courage to admit it. If she is making you nervous and you are not enjoying it then I personaly would send her away to be sold. With a proffessional rider on her she will show herself better to potential purchasers.
Do your best to get her a suitable new home and you will have done the best for you and her.