delete and block on fb. You have given her back her things she asked for, you have sold the things that were legally your/gifted to you by her ie. saddles. Hope you work it out!
If she gets stroppy cease contact and tell her that you don't want her to visit again. (Your horse, your rules). If she's OK then maybe let her visit, but keep all the stuff locked up. If need be remind her that none of the things she is asking about belong to her, including the saddle she GAVE you. Just as you can't prove she gave you a saddle, she can't prove that she didn't.