I sold my pony two months ago now they want to send her back?!!?

It's entirely up to you - if you are not in a position take the pony back you can refuse - any private sale carries the 'caveat emptor' umption and the onus is upon the buyer to ensure that the pony is free from any major health problems at point of purchase - presumably she could have had the pony checked out by a vet. Similarly any behavioural difficulties should have been checked by the buyer prior to purchase. I think the buyer has very little recourse despite what she says, and is playing on the fact that you have stayed in touch. You have a perfectly reasonable explanation as far as I can make out, so I would not worry about being made to take back the pony. I suspect your problem may lie with the feeling that the pony will be extremely unhappy with the current owner, but there's no-one who can resolve that issue but yourself....