Think the best suggestion here is just don’t leave the “door” open. No extra chair(s) or coffee mugs on display, pull one out only if needed, no cream or sugar or snacks) on display . Dont give her your ear, don’t stand and listen, just creates a target. Remove the target.
Same with tack, don’t leave it out unless you are using it, if Debi asks to borrow something, you don’t have one for her Do NOT get sucked into a discussion, the answer is no. Period. Not a negotiation, its no. Then walk away.
When people ask me if Ive seen their tack, I always say “ No, but I wasn’t looking or thinking about your tack”. End of discussion. Thats direct but, IMO, not rude for a random person you aren’t close to. I don’t say I am sorry to people like this either, not apologizing for their disorganization,
In trying to be nice to some people, you enable them to continue. No reason at all to continue when its not a friend or family member but a pest who tries to use you. Shes not going to stop it but you can if you stop allowing her to use you and suck the fun out if your horse time.